All things considered, the Celtics have had an extremely successful first half of the season. They sit atop the Eastern Conference with a four-game edge in the loss-column on the Miami Heat (and three on the Lakers).

Rajon Rondo has built on his impressive playoff showing and become a more consistent playmaker. Kevin Garnett has reverted to as close to 2007-08 form as anyone had a right to expect. Paul Pierce and Ray Allen have been remarkably consistent, and injury-free.

The Celtics are also back near the top of the defensive rankings and have sustained their incredible shooting percentages. They have also demonstrated an ability to beat the best teams in the league with wins over the Heat, Bulls, Magic and Spurs.

There’s a lot to like about the Celtics season, which reaches the midway point Wednesday night against the Pistons. But in the top-heavy Eastern Conference, which features no fewer than four legitimate championship contenders, there is still work to be done.

Here are five questions to ponder as the Celtics reach the midway point:

CAN KENDRICK PERKINS COME BACK AND BE THE PLAYER HE ONCE WAS?

Back in the summer when the Celtics signed the O’Neal brothers, team president Danny Ainge suggested that when Kendrick Perkins came back from knee surgery he would have to earn back his starting position.

As late as December, Doc Rivers was tempering expectations for Perkins saying — rightly — that there’s no guarantee for players coming back from significant injuries.

Then Sunday happened. With Jermaine O’Neal seeking a second opinion on his injured knee and Shaquille O’Neal felled by some wayward ice, Perkins returned to live practice and rejoined the starting fine.

By all accounts, Perkins looked good. He’s slimmer, stronger and still a bad man, as evidenced by his screen that sent Marquis Daniels to the sidelines.

“It was loud. I mean that in a very complimentary way,” Rivers said of the session, which was the first one with the old starting five since the NBA finals. “[Perkins and Garnett] were holding everyone accountable.”

Rivers said he aired out the second unit, but then he sat down to watch the film. “When I watched the practice film I realized that there was not a lot they could do,” he said.

Perkins has targeted Feb. 4 against the Mavericks as his return date, which would mark a relatively quick comeback from anterior cruciate ligament surgery.

That’s all good news for the Celtics, but the scary part is that was once thought of as a luxury has suddenly become a necessity. The Celtics need Perkins because their frontline depth has been decimated.

Jermaine O’Neal’s status is in doubt. Shaquille O’Neal is the definition of day-to-day and while Semih Erden has shown some flashes for the future, he’s also wandering through the rookie desert plagued by inconsistency and his own list of injuries.

As for Perkins role when he does return, Rivers tipped his hand after the Magic game while talking about the second unit saying that Shaq and Glen Davis would make a formidable backup frontline. That would make Perkins the starter again, which is a long way from the summer projections.

Perkins’ performance in practice was enough to forget about tempering expectations and start dreaming wistfully of a full-strength starting five. But if this season has taught us anything it’s that it’s dangerous to imagine the Celtics as a complete team because that hasn’t ever been the case.

Still, if Perkins can come back and be the same menacing defensive anchor then that would change the equation significantly.

“It’s going to help our starters but it’s really going to help our bench,” Rivers said. “The starters are the starters. They’re going to be good regardless. When you can have Baby and Shaq with Nate [Robinson] and Delonte [West], that’s good for us.”

CAN THE BENCH COME TOGETHER?

So much of this hinges on health, but the Celtics reserve unit has been a liability this season. They’re ranked in the bottom third in points, rebounds and assists according to data compiled by Hoop Stats.

The problem is that Rivers hasn’t been able to roll out a consistent lineup. He envisioned a two-platoon team with Delonte West, Nate Robinson, Marquis Daniels, Glen Davis and Shaquille O’Neal coming off the bench but that group has had to start 51 games.

Injuries to West and Rajon Rondo forced Robinson into a point guard role for which he is ill-suited. Injuries forced Davis into the starting lineup, which robbed the Celtics of their best reserve and Davis of one of his best assets: his versatility to play the four and five.

Injuries have also forced Rivers to use rookies Luke Harangody, Avery Bradley and Erden before they were ready with mixed results. Then there is Shaq who was supposed to be the low-post scoring option the bench has lacked since Leon Powe left, but he became the starter in training camp.

The one constant for the Celtics bench has been Marquis Daniels, who is their only legitimate option behind Paul Pierce at small forward.

Ranking just below Perkins’ return on the importance scale is that of West, who the Celtics need to be the backup ballhandler. West hasn’t set a target date yet, but he has been gradually increasing his basketball activity as he attempts to come back from a broken wrist.

Until Perkins and West come back there is no way to judge the second unit. Their play will be a major focus of the second half of the season.

CAN PAUL PIERCE AND RAY ALLEN KEEP IT UP?

The following players who play more than 25 minutes a night have a higher True Shooting percentage (which combines two-pointers, 3-pointers and free throws) than Ray Allen: Tyson Chandler and Nene who do most of their scoring via dunks and put-backs. 

Even for Allen his shooting has been remarkable this season. He is over 50 percent from the field and is making a staggering 48 percent of his 3-pointers, aided by a surreal 70 percent mark behind the arc in January. 

Pierce’s story has been slightly different. While he’s also having an extraordinary shooting season, he is also going to the rim and finishing at a comparable rate as LeBron James and Kevin Durant.

The two ageless superstars are in the midst of late-career career years, and perhaps most impressively, neither of them has missed a game while averaging about 36 minutes a night apiece. It’s only fair to expect some kind of regression over the next 41 games. The question is: how much? 

CAN RAJON RONDO BECOME A COMPETENT FREE THROW SHOOTER?

The single biggest weakness Rondo has is not his jump shot. It’s his free-throw shooting. Simply put, an All-Star NBA point guard should not shoot 46 percent from the line.

Rondo’s field goal percentages have held mostly steady with a spike in long-distance shooting, but he is getting to the rim and the free throw line at the lowest rates of his career, which means he is attacking the basket less than he has in the past.

There are a number of factors at play. His injuries have robbed him of his explosiveness at times. He has steadfastly passed up layups in transition for assists. But the most worrisome angle of this is his free throw shooting.

Rondo has played 29 games this season. In only seven of those did he get to the line for more than two free throws and he has played 11 games where he didn’t get to the line at all. As well as Rondo has played, this has the potential to be a severe liability.

HOW MUCH IS HOMECOURT WORTH?

Ever since the Game 7 loss in Los Angels to the Lakers, the Celtics have talked about the importance of getting homecourt advantage. They are well-positioned to make a run at securing homecourt, but the second half will have some major landmines thanks to the schedule.

After Wednesday’s game with Detroit, the Celtics will have only 18 games left at TD Garden and they have two long west coast trips still ahead of them.

There are nine remaining back-to-backs and eight of those will be on the road in the second game. There are 17 games in March and eight in 13 days of April. Additionally, the Celtics have seven games left with the Heat, Lakers, Magic, Bulls and Spurs.

Somewhere in the middle is the delicate balance between staying healthy and competing for homecourt. This has been the key coaching question that Rivers has faced this season and it will come into larger focus in the second half.