As others have mentioned, our starting 5 to begin this past season was: Irving, Brown, Hayward, Tatum, and Horford. Brad was taking a bit of a leap of faith by starting both Tatum and Brown, but both players have progressed better than anybody could have hoped. I don't see any possible way either one of those players goes back to the bench, especially after another summer working on their games.
The bench will be the real key. We could lose: Smart, Baynes, and Monroe. Another team might want to trade for Terry. It looks like Bird might be making a name for himself, Ojeleye could continue his 'hot' shooting of late, and Theis will be ready to continue his impact.
I can't imagine there will be as many 'fireworks' this summer as there were last, but there is certainly a lot to look forward to.