Here's the important numbers...
Hard cap: $143M
Tax: $136.6M
Just looking at the situation(I don't think these numbers are 100% correct but they're close).
Got the contract numbers from...
https://en.hispanosnba.com/salaries/miami-heat$36,016,200 Jimmy Butler
$28,571,429 Kyle Lowry
$28,103,500 Bam Adebayo
$15,517,242 Duncan Robinson
$ 7,500,000 P.J. Tucker
$ 5,214,583 Ryan Anderson *
$ 4,736,102 Kendrick Nunn
$ 4,004,280 Tyler Herro
$ 2,320,044 Dewayne Dedmon
$ 1,782,621 KZ Okpala
$ 1,620,564 Max Strus
$ 1,620,564 Gabe Vincent
With 11 signed, Miami needs a minimum of 3 more players under contract for the 14 man roster(max 15)
So as of now $132,271,027, leaving 4.4 mil under the tax, just under 11 mil under the hard cap.
FYI - The minimum for a 0 exp player is under 1 mil a year, adding 3 of these players leaves 1.4-1.5 under the tax(for now) and 8 mil under the Hard Cap.
Here's a link for salary minimums...
https://basketball.realgm.com/nba/info/minimum_scaleSo if Miami S&Ts Nunn or Oladipo up to 12 million, they can bring back 15 million in salaries but the Hard Cap only would limit Miami to 13 available to come back. You could add KZ and/or Herro to the package make it possible to bring back more(like a draft asset).
Also with Oladipo's Min looks to be $2,389,641 so if Miami wants to retain his rights and keep him with the team for the min, that's the number.