The questions for me are how he will adapt to the NBA pace, and on his decision making. But I am certain he will work hard, and will sacrifice his body for the team.
As for almost every rookie, the pace will be a shock. But he's made for it - that and the much bigger space that the NBA game takes place in.
Decision-making (a subset of a bigger category called 'feel for the game') is a big issue for him - agree with you there. Actually, I think that a lot of what has been interpreted as a lack of feel for the game is really a lack of skills – including skills that can be developed. For example his weakness in dribbling, and especially with his left hand, had him dribbling into a crowd and trying to force something where it wasn't available. His coach says he has a great feel for the game – go figure, and for what it is worth.
"Working hard" - looks like a given with him. Add to that: coachable, fanatically disciplined, team-oriented. Mature beyond his young age. As a professional, ready to join an already high-functioning Celtics locker room.