What do the Celts need?
First you have to answer what the Celts have.
Right now, the way I see it is that the Celts have an above average starting point guard in Isaiah Thomas. They've got a solid starting wing in Jae Crowder. They've got a decent but replaceable starting shooting guard in Avery Bradley.
Aside from that, they've got a handful of decent bench players.
Smart and Turner are capable backup ball-handler options; one is more defense-focused and the other is more of a shot creator.
Kelly Olynyk, Jared Sullinger, Tyler Zeller, Amir Johnson, and David Lee are all productive backup-caliber big men that each has significant strengths and significant flaws.
Conclusion:
- The Celts are pretty well off at point guard and wing.
- An upgrade at shooting guard wouldn't hurt but isn't a major need
- The team really needs a couple of no-doubt starting caliber big men
So I think if you added a forward like, say, Danilo Gallinari, and a big man like, say, Derrick Favors, and those two became the starting frontcourt, that would fill the biggest needs the team has.
All of the above is approaching the "What do the Celtics Need?" problem on a positional basis.
The other way you could look at this is by asking what the Celts are good at and what they are not good at.
Good:
- 12th in Offensive Rebound Rate
- 8th in Assist Ratio
- 2nd in Steals
- 1st (tied) in Opponent Turnovers
- 3rd in Opponent 3P%
- 7th in 3PA
Bad:
- 25th in 3P%
- 23rd in FTA
- 24th in Defensive Rebound Rate
- 18th in Blocks
- 23rd in Points Per Shot
The answer based on those rankings appears to be that the Celts really need to add players that can control the boards on defense, block shots, get to the free throw line, hit a high percentage of shots from outside, and generally score with efficiency.
All of that is consistent with the above -- adding big men who can rebound, protect the rim, get to the line, score with efficiency, and ideally also help space the floor would go a long way toward shoring up the team's weaknesses.
That description basically limits the selection to All-Star caliber big men, however, possibly the hardest type of player to acquire. It definitely helps you understand why Ainge was so keen on acquiring Kevin Love, though. He would have checked off a lot of boxes.
Upgrading the shooting guard spot with a player who can provide similar scoring and shooting as Avery Bradley while also attacking the rim and getting to the line more frequently would also help.
But again, that's probably an All-Star caliber player, and shooting guard is probably the shallowest position in the league talent-wise.
Taking your premise into consideration.
Would you try to trade for Tyson Chandler? Always an injury concern and on a long contract (which might tie up quite a bit of our cap space, but maybe enough would still remain regardless?).
A 3-man rotation of Tyson-Amir-Sullinger should solve some of your concerns. I'd assume Olynyk would still remain so you have his outside shooting as well. And there's Mickey coming up soon.
With the assumption that Amir won't stay around after this season, having a player like Tyson along with the young players we already have in the 4-5 spots might make a lot of sense particularly if you figure that Sullinger's best position is as a center (it's seeming that way this season). So you give Tyson and Sullinger all the center minutes, and Olynyk and Mickey all the PF minutes with the exceptions of when we go small.
One of the biggest things about Sullinger and Olynyk is that they've never been paired with another big that would play with their strengths and cover their weaknesses. Almost always their whole careers have been about playing out of position alongside other PF types (or inexperienced/weak centers). So I'm curious how the presence of a Tyson Chandler type would work for these two.
Now, that's just in theory. In practice... well... Chandler is 33 years old already and has always been an injury concern.
But just putting it out there for someone that might be attainable and probably not expensive to get (trade assets wise) while checking off some of the concerns you mention.
The other aspects you mention seems a bit harder to justify getting. Teams seem very reluctant to move players that can really score the ball, and those that can I'm not certain they'd be an upgrade over what we already have.
The real question is, who's Turner? Because if he's being aggressive and attacking the rim and more so if he's a facilitator instead of trying to look for his shots over and over (except when he's going strong to the hole, and maybe in post up situations) then chances are that a lot of what you are looking for he could fill. The other problem is that in his absence, who's running the offense? Hopefully Smart can step up to that role.
What I'm not seeing is an abundance of shooters at the SF spot, but at the SF spot it's also an area we need to improve defensively behind Crowder.
So the question then becomes, is someone like Lance Stephenson available and would you trade for him?
Clippers are using him, but not all that much. He's a bit behind in the depth chart. So something worth considering. He has a team option thought, and that may be of value as a trade asset. So that alone might make him untouchable. That said, I don't know when is the execution date of that team option, that may be critical to know what its real value is.
So those are my two suggestions for now: Tyson Chandler and Lance Stephenson.