Just my two cents on the Luka situation...Regardless of when he picks up his 4th foul he's sitting until the end of the game when he's absolutely needed, so with that being the case why not take your chance in the first half. You're giving up almost 13 first half minutes with your best player sidelined to "protect" him from getting into foul trouble in the second half.
I get the unwritten rule about sitting a player and do that with the youth team I coach, but that said you're taking your best player, and possibly the best player in college basketball, out of the game for 13 minutes. IMO there comes a point when you have to trust your player, weigh the current situation, with where you are in the game. As a coach can you find a scheme that minimizes his opportunities to pick up that 3rd if keep him on the floor?
Despite the fact we were up 10 we essentially sat him for over a quarter of the game just to be on the safe side. You can't play by what ifs, but do we continue to extend that lead if he stays on the floor in the first half? Would that lead be enough to squeeze one out in the end? Unwritten rule or not, I don't think you can take your chances sitting your best player for a 13 minute stretch just because you want to be sure he's available at crunch time. IMO you risk him picking up his 3rd those last 13 minutes of the first half rather than seeing to it you have him the last 5 minutes of the game.