The Celtics will have max. efficiency if everyone buys into the style of basketball that is best suited for a team with this kind of solid, but unspectacular depth.
Take full advantage of the cards you were dealt. They need to play up tempo, taking advantage of their ability to substitute often, without a serious drop-off in skill level. Play an unselfish style of ball, using ball movement to find the best option, rather than hero ball.
This team has a chance to be a good defensive team, everyone must buy into defending aggressively, without worrying about personal expenditure of energy. IMO, use IT as a weapon off the bench to score and push the pace of the game, on a defense that may be tired.
If they're blessed with the luck of good heath...yeah, I can see top 4.