it looks like you know your little guy really well - so that's actually the best thing for trying to make it through this switch (not that that helps much right now!) Let's see if I can answer your questions:
1. I would stick with the same hours of A time - that may mean different clock times - for naps and bedtime for at least 3 -5 days to see if that helps. Since he's always been on the low end of sleep, I'd go with 5.5 hrs of am A time, then nap, then do 5.5 hrs til bedtime and see how that goes. So if he wakes at 6, nap at 11:30 (hopefully til 1:30), then bedtime at 7.
2. Since you know that a 12 hr night messes up his day sleep, then yes, I would wake him after an 11 hr night - unless you want to try to extend your day (so it starts later than 6), then I'd wake him at the hour you want to start the day and run your 5.5 hr A time from there.
3. Pushing him til 12 for a nap would be 6 hrs of A time, and that's probably still a bit much. I think you probably could have pushed him til 11:30 though.
does that help? I wish I could make this easier!!!!