1. It will probably have minimal clearance, but if Terry says it will fit, it will.
2. I don't know, but why look for a different model? The Drake is a top performer.
3 & 4. Why would you opt for an AS OR any other brand over a Toto? Toto is the top performer.
Waste is not cleared from a drain with a single flush. No toilet flushes with pressure in the drain line. (Power assisted toilets use power to put the water into the bowl, not the drain) The 1.28 gpf will work just fine, assuming your drain has the proper slope of 1/4" per foot, or approximately 7-1/2" for the 30' run.