I know it's such an annoying answer, but for now the only "need" that matters on the Celtics roster is the lack of a star. The #1 goal is finding a high impact player to slot in long term. Until then, everything else is in flux, so there's not much point in worrying about the minutia.
Note that I'm not talking about a LeBron / Durant level guy. They need a mid-00s Pierce type player, then the conversation can shift to how we fill in the other gaps and get good supporting / complementary core pieces.