The big question facing the Celtics this preseason — really the biggest preseason question in the whole NBA — concerned the health and well-being of Kevin Garnett. Those questions appear to be answered. KG is back.

Garnett appeared in six of the team’s eight preseason games and averaged 12.7 points and six rebounds in 21 minutes of action, shooting a healthy 56 percent from the floor. That was all well and good, but Garnett distinguished himself by running the floor, taking a few bumps along the way and displaying his trademark explosive athleticism toward the end of the exhibition season with a few well-timed dunks.

With Garnett coming off his first major knee injury, it’s really quite remarkable to see where he is as a player. There were times early in the preseason when Garnett looked a little tired and stiff. Doc Rivers assured everyone that it was just natural rust and once he worked himself back into playing shape all would be fine.

The skeptic in all of us took note and watched closely. Sure enough, his legs and jumping ability slowly began to return as the October games rolled on and the old Garnett began to reassert his dominance.

That said, it would be a mistake to think that Garnett is ready for 36-40 minutes a night of the 82-game NBA schedule. Fortunately for him, and the Celtics, he doesn’t need to log those kind of minutes with the addition of Rasheed Wallace. Rivers can afford to monitor Garnett’s minutes and keep him in the 30-32 minute range over the course of the season.

Rivers has been most judicious about not overworking Garnett, but the Celtics suffered a noticeable drop in production last season when he was off the floor. That should change with Wallace around, but if we learned anything from the playoffs last season it’s that the Celtics are not a true championship contender without Garnett.

They need to have him healthy and ready once the playoffs start, which will be an ongoing part of the Celtics conversation throughout the winter. But Garnett passed the first test and appears ready to start the season with few restrictions.

THE BENCH IS SETTLED

Flash back to late May. With Glen Davis in the starting lineup and Garnett and Leon Powe in street clothes, Rivers cast a forlorn look down his bench to find Stephon Marbury and Mikki Moore staring back at him. Gulp.

Rivers’ bench options during the playoffs primarily involved Eddie House, Brian Scalabrine and a whole bunch of hope. No longer. Davis is back in a backup role where he can come in and provide energy and a jump shot for 18-24 minutes a night. House is House, which means a steady diet of catch-and-hop 3-pointers.

But the additions of Wallace and Marquis Daniels look like they will not only add scoring punch, depth and defense to the second unit, they also look like they will solve many of the problems the Celtics had before everyone started getting injured.

The two obvious names missing from the 2007-08 championship team were James Posey and P.J. Brown and while Daniels doesn’t quite offer the same package of skills that Posey had, he can do many of the same things defensively. That is, guard multiple positions.

Wallace, meanwhile, does many of the things that Posey did offensively, namely stretch the floor with his long-distance shooting ability, and he has the size that was sorely lacking without old reliable P.J. As an added bonus, Daniels appears to be the slasher that the Celtics hoped Tony Allen would be last season.

That gives Rivers a nine-man rotation, which is more than enough, but he still has Scalabrine to break out in case of an emergency and another backup big man with size in Shelden Williams.

The missing piece, as it was last season and the season before that, is a proven backup veteran point guard. In theory Daniels and House can handle the position but don’t count on too many opposing teams allowing them the luxury of bringing the ball up the floor without exerting pressure.

In each of the last two seasons Danny Ainge reached out and brought in former All-Stars, Sam Cassell and Stephon Marbury. In truth, neither was a particularly good fit, although Cassell did have his moments. It won’t be a good sign if Ainge has to go to that well again this season.

RAJON RONDO LOOKS TO BE IN A GOOD PLACE

Unlike his more celebrated teammates, Rajon Rondo rarely offers glimpses into his psyche either on the court or when he talks to the media. So, we are often forced to guess what is going on inside Rondo, which can be a dangerous game.

That said, after an offseason in which his coach and GM dished out some tough medicine, Rondo came into camp in great shape and seemingly great spirits. This is a big year for the 23-year-old point guard and not just because of his looming contract extension.

There are many people, myself included, who feel that he is already the best point guard in the East and there are just as many who wonder if he’s really legit. Rondo should be past all that by now, but the hole in his game — his outside shot — is so obvious and glaring that he will have to prove it again and again if he is able to win over his detractors.

Rondo has already moved to the front of the defensive class, but even there he has some bad habits he needs to break, such as reaching for steals.

“At times last year he put himself in bad position and that drew fouls on him,” Rivers said earlier in camp. “Sometimes he drew fouls on other teammates and that’s just as bad. He has such a great innate ability to read things before they’re there so you do have to give him some latitude.

“He could be great. Defense for coaches and defense for the outside world are two different things. If you want to make the All-Defensive Team, just get steals. Play no defense and just gamble and they’ll recognize you for All-Defense. But if you want to be a great team defender do that plus do all the other things and when you do go for steals you never put your team in harm’s way and I think Rondo this year had done a terrific job with that.”

Rondo will continue to be the most heavily critiqued and criticized player on the Celtics roster this season. That’s partly because his game is so unique that it defies easy descriptors and labels. It’s also partly because of his status in the Celtics pecking order, but he is arguably the second-most important player on the roster, after Garnett, and frankly, there is no limit to where he can take this team.

DON’T SLEEP ON PERK

Throughout the Summer of Rondo very little attention was paid to the Celtics center, who it must be pointed out is still three months younger than rookie Lester Hudson and is entering his seventh NBA season.

That’s nothing new for Perkins who has been the forgotten man throughout his tenure in Boston. Even before the dawn of the Big Three era, Perk took a back seat to Al Jefferson, Delonte West and even Gerald Green. But if last year’s playoffs served as a coming out party nationally for Rondo they were also something of a crucible for Perkins who battled Dwight Howard to the very last minute with only one good shoulder.

The series against the Magic solidified Perk’s rep as a defensive force, but he came to camp slimmer and faster and showing a smooth assortment of low post moves. There were still too many times in the preseason when Perkins fell back into his old bad habit of bringing the ball down to the floor with a power dribble instead of simply going up strong and finishing plays, but there were just as many times when he looked downright fluid scoring down low.

The Celtics don’t need Perkins to score, but they do need something of a low-post presence and you can make an argument that Perkins is their best option. Even before he got hurt Garnett’s game had drifted almost exclusively out to the perimeter and Powe is now in Cleveland rehabbing from his latest knee injury.

Perkins can get 10-12 points a night simply on put-backs and running the floor, but if he is able to add a low-post touch to his game that will make the Celtics that much more dangerous in the halfcourt.

THE CHALLENGE AWAITS

The Celtics are no longer the defending NBA champs. They are no longer the beasts of the East for that matter. Their 2008 title and 19-game winning streak last season are all distant memories as they get ready for this season.

The Cavs loaded up with Shaquille O’Neal and Tony Parker. Orlando brought in Vince Carter and Brandon Bass. Washington looks to be much stronger with Mike Miller and Randy Foye along with the return of Gilbert Arenas. Even the Hawks made smart moves in the offseason getting Jamal Crawford and ageless Joe Smith to round out their bench and provide real depth.

With the uncertainty of the mega 2010 free agent class drawing near as well as the possibility of labor unrest after 2011 this NBA season promises to be one of the more intriguing in recent memory. The have nots are many, but the haves are all loaded and, on paper at least, improved from last season.

Barring a complete collapse or an unfortunate run on injuries the Celtics will finish anywhere between first and third in the East. Time will tell how much energy and minutes they exert for their final playoff positioning, but as the regular season awaits they have answered all of their important preseason on-court questions.