The interior layout is shown in the floorplan. My strategy was to keep everything as open as possible so as to avoid the fate of most RVs - i.e. ending up a hallway on wheels. The typical RV layout is a narrow walkway running down the center from front to rear, with a series of alcoves, appliances, storage and furniture lined up along either side. It's terribly cramped. I also wanted a full-size kitchen and bathroom, much better suited to full-time living than the closets normally found in RVs.
One feature that I did particularly like in commercial RVs was the over-cab loft. It's a very efficient use of space. I would hate to dedicated that much of my limited floor area to a bed. Stacking the sleeping area and the cab gives up some headroom in each, but since neither is used standing and both are used intermittently, it isn't much of a sacrifice.
Outside of just providing amenities, there are two immediate problems with full-time life in an unmodified school bus. One is that the ceilings are low and the space is cramped. I'm short enough to at least stand up straight, but anyone much taller than me would have to stoop. The other is that school busses have terrible insulation. Once you account for all the glass too, the amount of heat loss is absurd. In some climates it might be acceptable, but the heating costs during a Michigan would be unreasonable.
The best way to deal with all this is in one fell swoop: a sawzall, a welder, and major structural changes.
After stripping the original interior, the next step was to raise the roof. This was as large a project as one might suspect. I ground off the front cap and the rivets along one seam in the roof. My dad and I cut through the ribs and hoisted the roof up onto a wooden scaffold, which would support it until I completed enough welding for it to be free-standing again. I welded in spacers at each rib, framed a loft extending over the cab, and built a very heavy-duty support structure at the transition.
From the rear wheels forward, I now have an extra 2' of vertical height. 1' is lost to the raised floor under which my water and waste tanks are stored, but the extra 1' of headroom makes a world of difference in how spacious the bus feels. The extra height also gave enough room to build the loft I had hoped for.
The transition in roof height also provides a degree of separation between the living area in the front and the kitchen and bathroom in the rear without actually closing them off.