Ideal and realistic are both entirely different concepts. But I will bite and try to go for my 'ideal,' realistic team.
S&T Wanamaker of about 8 million, with the 2nd or 3rd year non-guaranteed. (He does this, because he gets a lot of money upfront, plus he gets to stay in the NBA, and he'll also see plenty of minutes considering the lack of depth at the PG. Similar to how we did the Keith Bogans deal.)
Waive all cap holds with the exception of Horford/Irving/Morris and of course Wanamaker.
Yabusele, Tatum, Williams, Ojeleye+ Wanamaker equals to about $18.4 including the prorated deal of $4 million added with S&T'ed Wanamaker.
We could go either 3 ways, but this isn't even taking into account the fact AD would need to waive the trade kicker:
Add $6.5 of the contract for Jaylen Brown, who would cover the necessary cap space.
Sign and then trade draft picks that would equal to 7 or $8.4 (assuming Ainge gives draftees the additional 20% incentive increase.)
Use Marcus Smart $12.5 contract instead of Brown's.
I would go with the draft picks, Yabusele, Williams, Ojeleye, Tatum, and S&T Wanamaker for AD.
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KD opts in, and we match his salary by trading Horford after he opts in as a straight up deal.
If GSW is unwilling, we could go both ways, we could offer Jaylen Brown as a sweetener in exchange for Quinn Cook + Bell or Looney. So now you're pretty much left with Baynes, Kyrie, Smart, KD, Hayward, and maybe Theis. (He reportedly went back to Germany to train, but has said he isn't sure if he is coming back.)
I would like to re-sign Morris for about $10-12 million. Bring in his brother if he wants, in that case we could up Morris's contract to $12-14, and they can both split the money evenly.
I would see if maybe Tony Allen, Kyle Korver, Shane Larkin, and any other role players/ring chasing vets like Carter, or Perkins would be interested in coming as a mentor/player coach or leadership.
Sign Jared Dudley, and try to see if you can swing for the fences and bring in JaMychal Green for the MLE.
You're left with
Kyrie
Smart
Durant
Hayward (KD has voice displeasure at being at the 4. I think Hayward could be the prototypical swing or point forward.)
AD
Larkin/Cook
Korver or Allen
Carter
Dudley or Green/Bell
Baynes/Perkins
My math may be slightly off. I just guestimated this, currently at work, but was bored of doing taxes.
I assumed Brown is headed to either GSW or NOP, so can swap whichever is necessary.