RealGM

As the Celtics do well, their players look increasingly valuable.

Tatum is a Supermax player.
Theis is getting lots of recognition around league as having been (until now) underrated. His next contract will be for significantly more money, albeit somewhat limited by the low-ish number of minutes he plays.
Smart is one of the Celtics stars of these playoffs. His next contract will be for more money too. (And more than Theis'.)
Hayward can't return to the lineup soon enough.
Even Wanamaker is looking somewhat like a keeper, and not just at vet minimum.

The Celtics are a contender, and contending is expensive.

Meanwhile, 2020-21 looks to be a low-revenue season, because of the pandemic.

I THINK ownership will spend to keep the team together and perhaps judiciously add to it. If the Celtics don't at this point spend to contend, who will? But really, it's hard to be sure of anything. In particular, salary-dump trade proposals seem premature, except perhaps for those in the vein "Let's try to bundle our least useful players and picks into a package for one guy who'd actually crack the rotation."

I’m not concerned about losing Theis or Wanamaker, both are easily replaced. Smart is going to be tough. I would love to keep him but you are absolutely right. The way he’s been playing lately he will get a significant raise when his contact is up.

Tatum is a supermax player and signing him will need to be a top priority.

21/22 has wiggle room but next year moves need made, thies is a lock next year for 5 mil. And green is a lock to waived. Poirer was a mistake signing that was being explored for years prior not to mad about it worth a shot. Edwards signing seems to be managing the lower half the roster due to exactly your post statements. Got to have bodies on the cheap ie: semi to cheap not to sign. Hayward and enis likely opt in then sorts itself out of those contract. The big heavy is kembas contract that hurts. Tatum gets Max and I'm cool with that. Lots to ponder about Id keep thies though