problem with floating walls
I am thinking that sheetrock should overhang (here, the bottom edge of the plate) no more than an inch.
You could put metal kick plates on the door bottoms to span most of the space under the doors.
Having the lower edge of the wall move back and forth an inch or so because it is not fastened to the floor slab is always a problem. ONe way to combat that is to put doorways only where two walls come togehter at an angle. Closets at strategic locations will give you more wall sections that come together at 90 degree angles.
The disadvantages of crab apple trees. In summer, the apples are too sour to pick and eat. In winter the birds come and leave dropping all over the place.