The first item of business for Celtics president Danny Ainge was locking up coach Doc Rivers to a long-term contract, which they agreed upon Friday for five years. With Rivers on board for more than just a last run with the big three, the Celtics will enter an offseason where they are looking at the long-term, while also trying to stay contenders for next season.

The real overhaul is likely to begin after the 2012 season when Kevin Garnett‘s contract comes off the books and a new collective bargaining agreement is in place. The 2012 free agency class in also much stronger than this summer’s crop with Dwight Howard expected to be the main prize.

Building around the core for one more shot at a championship is really the only option for Ainge unless he is willing to trade one of his aging stars. In an end of the season meeting with the media, Ainge said that he always considers all options. Still, it would be a surprise.

Assuming Ray Allen picks up his player option, which he said he intends to do, the Celtics will have over $64 million committed to six players. That would put them over the salary cap under the current rules and while they are likely to be altered under a new CBA, the cap number is not likely to go up from its current $58 million.

“I know this about the big three: they still have a lot of basketball in them,” Ainge said. “How much can they carry a team, [and be] 20-point a game scorers, I don’t know. I do know they’re still very talented but we need to add talent around them.”

It’s important to note that no one knows what the new salary cap rules will look like under a new CBA. Therefore it’s impossible to predict what kind of moves Ainge will be able to make this offseason. Under the existing rules, Ainge would be able to go over the cap to re-sign his own players and offer free agents from other teams money from the mid-level and bi-annual exceptions, as well as the veterans minimum.

Before we get to a new CBA — and free agency — here’s a look at the current roster, with comments from Ainge.

PLAYERS UNDER CONTRACT: Rajon Rondo, Paul Pierce, Kevin Garnett, Jermaine O’Neal, Avery Bradley

Rondo: The All-Star point guard just finished the first year of a five-year extension. As he is no longer a base-year compensation player Rondo could be available in a trade, but Ainge said on WEEI’s The Big Show that he’s not looking to deal Rondo.

Ainge said that Rondo’s dislocated left elbow will not require surgery. He also recounted this tale from the locker room after Rondo hurt himself after he became tangled up with Dwyane Wade in Game 3 of the Celtics series with Miami.

“He was in an amazing amount of pain,” Ainge said. “He was trying to get back on the court now. He didn’t want to ice it. He didn’t want the X-ray. He said pop it back, tape it up, let’s go.”

Rivers decision to return for the long-term binds him and Rondo together through the inevitable transition period. How Rondo grows and develops as a player and a leader will be the key for the next Celtics era.

Pierce: Much was made of Ainge’s comment on The Big Show that Jeff Green could start ahead of Pierce. Ainge backed off that on Friday.

“I said that on the radio show yesterday to get everybody excited,” Ainge said. “I’m sure I’ll be hearing from Paul. I don’t know, that will be Doc’s decision. Jeff playing a bigger role if he comes back, I think that will be the case. I have no idea [how that will work], maybe he’ll start in place of Ray. Now I’ll be hearing from Ray. There’s some things that can be tweaked. That’s my whole point.”

Here’s the real takeaway from those comments. The Celtics never planned on having Pierce and Allen play 36 minutes a night for 80 games this season. That they were able to at this stage of their careers, is an immense compliment to their conditioning and competitiveness. The flipside of that is they had to play that many minutes because the Celtics bench was in a constant state of flux given injuries to players like Delonte West, Marquis Daniels and even Von Wafer.

“I think that’s an unreasonable expectation to expect them to play the minutes they played this year,” Aineg said. “That was not in our plans at all this year for them to play as many games as they did and as many minutes as they did. Unfortunately we had injuries to everybody else. It was amazing that those guys were the most durable. I think our plan going into next year will be less games, less minutes.”

Pierce had his best season since 2007-08 and stayed injury-free in the process. He’s signed for another two seasons with an option for a third. It may not be realistic to expect Pierce to duplicate his post-prime success in the future, but he will need to continue playing at a reasonably high level if the Celtics can remain contenders.

Garnett: In many ways this was an inspiring comeback season for Garnett who returned to elite levels as a defensive rebounder and defender, while missing only nine games due to injury. Unfortunately for Garnett, the postseason left a terrible aftertaste. He performed brilliantly in Game 3 against Miami, but couldn’t duplicate his offensive success in the next two games.

“I saw a guy that played great defense in our series and is the catalyst and the leader of our defense,” Ainge said. “I thought he was unbelievable in Game 3 and then Game 4 and Game 5 he wasn’t the same offensively. That’s going to happen. KG is not expected to have to carry us. It would be nice if he scored 28 points every night but we just don’t expect that out of KG.”

Rivers has kept Garnett on a strict minutes limit during the regular season. Expect more of the same next season, and it wouldn’t be a bad idea if he emulated Spurs coach Gregg Popovich‘s approach to Tim Duncan, which includes sitting him out for one game on back-to-backs and maybe even keeping him out of practices.

Garnett has one year left on his contract, which will pay him over $21 million. Once his deal is up, the real overhaul will begin.

Jermaine O’Neal: Considering what he was able to do in the playoffs, the Celtics would love to have O’Neal back for the final year of his two-year contract. Yes, the pendulum has swung that far after O’Neal was able to play in only 24 regular season games.

Ainge said O’Neal will need surgery on his left wrist, which he fractured in Game 1 of the New York series while he was taking a charge. The injury affected his ability to finish inside, but he still had his moments in the playoffs, both offensively and defensively.

O’Neal said after the Celtics were eliminated that he would take some time before deciding whether to return. He also noted that a potential lockout could change his plans if it drags well into next season. The early guess is that he will come back and if he can give the Celtics 20-25 minutes and 60 games, it would be a big help.

Bradley: It wasn’t a total wasted year for the rookie who now has a season of professional basketball under his belt and who also performed well during a stint in the D-League. The Celtics love his potential and now he needs to take a positive step this summer in his development. “I’m looking for Avery to make some good improvement this summer and come into training camp ready to win a job,” Ainge said.

The Celtics need to get younger and more athletic and Bradley will have every opportunity to carve out a reserve role.

PLAYER OPTIONS: Ray Allen, Shaquille O’Neal

Allen: The sharpshooting guard said after Game 5 that he intends to remain with the Celtics. Assuming he picks up his option, there may not be a better veteran bargain for $10 million. As with Pierce, the Celtics may look to manage his minutes during the regular season. Look for this area to be addressed in free agency. The Celtics never did have a reliable backup behind Allen this season and they had no one who could duplicate his 3-point shooting off the bench.

Shaquille O’Neal: It’s very likely that we have seen the last of Shaq who simply couldn’t come back from an Achilles injury that kept him out for all but 17 minutes after February 1. Ainge acknowledged that the team believed Shaq was coming back before he made the Kendrick Perkins trade.

“Shaq brought us our best offense that we’ve had in four years when he was healthy and playing well,” Ainge said. “We had every indication from Shaq, from doctors and trainers that Shaq would be healthy and should have no issues by the trade deadline. That changed. Maybe we should have taken his age into more consideration.”

Shaq does have an option to return for the veterans minimum and no one should ever say never in this league, but his return looks doubtful.

RESTRICTED FREE AGENT: Jeff Green

Ainge said that he wants to retain Green and that he believed Green will play better with a full training camp and a larger role next season.

“I think Jeff played excellent,” Ainge said. “Maybe the expectations were too high. We knew he wasn’t going to start. We knew he wasn’t going to play 35 minutes. We needed a veteran player, an experienced player, an athletic player. We know what Jeff Green is. He’s a highly efficient offensive player who plays good defense. That’s what we need and he’s young and I think he’s just going to get better because of his character and work ethic.”

It’s clear that Ainge considers Green an important part of both the future and the present. They were never able to give him a clearly defined role and playing behind Pierce, Garnett and Allen, it’s still unclear how they intend to do that. If Ainge is right about Green, he may hold the key to next season.

FREE AGENTS: Glen Davis, Delonte West, Nenad Krstic, Von Wafer, Troy Murphy, Carlos Arroyo, Sasha Pavlovic

Davis: At one point this season, Davis’ future seemed secure. He was enjoying the best season of his career and was mentioned a legitimate sixth man of the year candidate. Then he went into a terrible slump at the end of the regular season that carried over into the playoffs and left him asking about himself in the third person.

“We like Glen,” Ainge said. “We didn’t look at this last month where he didn’t play as well as he was capable of playing, but we have to look at the whole package of what Glen has given to us a player. I think there’s a lot of mistakes made on players who play well in a playoff series and players who play poorly in a playoff series. I’ve seen a lot of teams make mistakes made over the years based on that kind of performance. We’ll take his whole  career under consideration as we determine what short of price he’ll demand and that he will definitely look at the market and see what’s out there for him.”

There’s no question that Davis tried Rivers’ patience as well as his teammates during the playoffs. That doesn’t preclude him coming back at the right price, in the right deal. The Celtics need talent and for all his maddening inconsistency, Davis does have talent. If some team swoops in and offers a big-money deal and the chance to start, he would probably be gone.

The Celtics let the market come back to them when Davis was a restricted free agent after the 2009 season and that’s likely to be the same scenario this time around.

West: It’s not a foregone conclusion that West will return next season (see: Tony Allen), but assuming the two sides can work out a deal, it seems likely. West has never been able to avoid injuries during his career, but last season reached almost absurd levels between a broken wrist, a fractured bone in his foot and a shoulder injury.

The Celtics know what they have in West: a tough, tenacious competitor who will play any role that’s asked of him. Re-signing him should be a priority, not an afterthought.

Krstic: Ainge had a quick, “Yes,” lined up when he was asked about bringing Krstic back and it makes sense. There simply aren’t that many 7-footers with offensive skills and his level of experience available on the free agent market. Ainge said that Krstic was finally healthy after a pair of knee injuries for the Miami series and pointed to his Game 5 performance when he scored eight points in 16 minutes.

A center combination of Jermaine O’Neal and Krstic along with another big body obtained in free agency wouldn’t be the worst way to fill the position. If Krstic does leave, that would open another roster hole with limited resources to fill it.

The rest: Of the four remaining free agents, Wafer and Arroyo probably have the best chance to return in that order. That will depend on what they do in the draft (they have the 25th selection in the first round) and in free agency. None are considered high priorities.