1. I use
Meg's Detailer line APC.
2. Your favorite wax

My choices would be Nattys, Paste Glaz, Nattys Blue, or #16.
3. Haven't used it. Can't really help you here. I'd wait at LEAST a few hours if possible. Sometimes you just have to leave.
4. I've only used Z6, and I don't recall any more/less
water spot issues than any other LSP.
5. Yes, I polish/wax my door jambs and engine compartment finish. I used
AIO/#16. Add some Gummipflege, and those door jambs look terrific!
6. It depends. I usually clean engines by hand with just car soap and water, cleaned with a cheap MF towel. Sometimes I use APC.
7. Yes there is a benefit to using
SG on your wheels, just like there is a benefit to using it on your paint. SG will protect your wheels much longer than AIO. I've got AIO/WGx2 on my wheels, and they're just starting to lose their beading action. That's OK though, because another week or so, and my wheels are coming off for the season.