I would wait to see if we can sign Hayward first before seriously looking at Butler or George. I don't think George and Butler are that much better than Hayward that it would be worth it making a deal when we may be able to sign Hayward without giving up assets. Also, if we get Hayward it would mean he's committed to staying. You cannot say the same for George or Butler if they come in a trade.
The second reason I'm wary of trying to make a deal for George or Butler is because they currently are on Eastern Conference teams. The Pacers and Bulls would definitely demand more from the Celtics than they would from a Western team.
Looking at the roster, if we are going to consider finances as being very important then you simply cannot trade Crowder as part of the deal. Smart, Thomas, and Bradley all have deals up after next season and unless we sign/acquire nobody this offseason it will be very expensive to keep all 3. Let's assume we keep Thomas at a max or close to max deal. Bradley will be at least in the 15 range and I'll just guess that Smart commands around 8-12 as a rough estimate. That is just too much money to be paying 3 guards as a general rule. Remember that Rozier is still signed for two more years after this season on a cheapo deal and has shown to be a decent backup.
So using that logic, it stands to reason any deal for Butler or George pretty much has to involve Smart and/or Bradley. Crowder is still signed for four years after this one on a super-low deal and as the Celtics move to become a real contender during that period, his contract will be invaluable because the team will desperately need cheap role players to surround their high-priced stars (Thomas, Horford, Player X?)
Put it this way, having a nice cheapo deal like Crowder's isn't worth as much on a rebuilding team like Indiana or Chicago's (if they deal George or Butler, those teams are definitely blowing it up) because those teams have no reason to save money. They're not going to be in salary cap trouble because they won't have any high-priced players on the roster anyway. So yeah, even if the Bulls or Pacers like Crowder, that will not be his primary value to a team that's trying to lose. His primary value is as an asset. A rebuilding team will not be able to win while Crowder is still in his peak anyway.