I can't answer all of these but I'll take a crack at a few.
1. It will be empty, you probably won't have to wait in line for anything. Some of the merchandise may be sold out, though.
2. I've only ever taken the bus, so I can't help with this one.
3. It depends on which corral you're in and how much you care about being towards the front of it. Corral A closes 20 min before race start (so 4:40am), corral B closes 10 min prior to race start. If you show up after your corral is closes youd just fall back and join a later corral. If it's important for you to be at the front of your corral I'd be there by 3:30 at the latest. Others who have more race experience than my measly two races should weigh in with better opinions, though.

4. There will be instructions on the back of your bib for linking to your photos. I don't think you need a magic band, it's all done by your bib number (but I haven't managed to stop for a character yet, so someone please correct me if I'm wrong!)