First, I wouldn't trade Saric, it's not just that he's goigg to get better (watch for major improvement in his 3 point shot, and he'll add strength), but there's the character issue, some athletes have that will to win, and Saric has it in spades, you need these guys to go with the stars.
Second, I wouldn't trade with Boston, for a number of reasons, they're Boston, you're dealing with Ainge, and you have to get through them to get to the finals.
Third, I'd wait and see if Embiid can stay healthy, if he can't, Fultz isn't going to make you a championship team.
Fourth, let's see how Simmons develops as well as TLC, Korkmaz, etc.
Fifth, if Boston takes Fultz, we can sign Bradley in FA after next season and laugh at Ainge. With Thomas and Fultz, you know Bradley will walk.