If the goal is to create max cap space, renouncing Kelly is not an option (unless we stash both Zizic and Yabu).
For the sake of discussion, let's assume we do the following :
1. trade Rozier - Jackson for draft pick(s)/salary relief
2. renounce Kelly - Amir - Jerebko - Green - Young
3. decline team option on Mickey
4. stash Yabu overseas/in the D-League
We will still have :
Horford - $27,734,405
Bradley - $8,808,989
Crowder - $6,796,117
Thomas - $6,261,394
Brown - $4,956,480
Smart - $4,538,019
SUM : $59,095,404 for 6 players
+ cap hold for the #1 pick : $7,026,240
+ cap hold for Zizic (#23) : $1,645,200
SUM : $67,766,844 for 8 players
Teams are assessed a $815,615 roster charge for each open spot below 12 players.
$815,615 x 4 = $3,262,460
$67,766,844 + $3,262,460 = $71,029,304 for 12 players
The latest salary cap projection has the cap at $101,000,000.
$101,000,000 - $71,029,304 = $29,970,696 available in cap space
The max contract for 7-year vets starts at 30% of the cap.
101,000,000 x 30% = $30,300,000
29,970,696 - 30,300,000 = -329,304
That is $329,304 short of Hayward's max.