1. Try to address it during a time out. Not really your place to kill the rally unless you are calling a specific violation within your realm of jurisdiction.
2. A reasonable amount of time. Your mileage may vary. Might wanna address this too while you're over there telling him to blow his whistle.
3. Probably, unless he's obviously pointing the wrong way on the point signal, then you might want to help get that right.
4. Be ready to take heat from the coaches.
Really, unless he's screened, it's his call. Don't make ball handling calls while umpire unless you're 100% (not 99%) sure your partner was screened and couldn't see it.
Others:
1. Talk about whether you want a post match debrief BEFORE your match. That way, you're just following up on what you agreed upon earlier. If you have a rough match, and then someone wants to talk, it might be taken defensively, so talk about it beforehand.
2. Yes, they were net violations under NFHS rules, and would probably have been let go under NCAA/USAV rules.