Is your bed up off the floor in the curvy part of your walls? Otherwise 7 ft floor seems kind of short to me (6 ft tall, plus pillow and a little room to stretch).
The advantage to a curved roof structure is the inherent strength of the arched shape and the ability to omit seams. A curved surface brings depth to the shape that adds rigidity.
That being said, plenty of simple, angular profiles have been quite successful. Build what you want, but don't be afraid of curves; they're not as difficult as they look, provided you don't go too tight on your radii and use thin enough ply. Even 5 mm ply can get down close to 13-1/2 inches radius w/o steaming (tho I had a little blowout in one spot). There are lots of examples of 1/8 inch, sometimes applied in multiple layers, going much tighter.
If you are not insulating and just want to build fast, simple 3/4 inch ply walls are okay (I guess

), but if you want the thermal (both hot and cold) and sound insulating properties, it makes more sense to take the time and build lighter with thinner skins using stick built frames or skeleton ply cores. Now there is a whole debate on what thickness outer skin makes sense. If you are off road a lot and concerned about puncture resistance from branches and brush you may want to consider 1/4 inch as the minimum (glued to the foam and frame). Most people agree that thicker is just added weight, but there are some guys that consider themselves hardcore wheelers who won't go less than 1/2 inch (seems excess for most usage to me). Street only builders have often said that they wished they had used only a single layer of 1/8, both inside and out. Consider thinner ply with aluminum rock guards in susceptible areas.
Most of my build is 5 mm, except the tongue box floor and galley counter top are 1/2 inch. I did a composite floor, hybrid foamie walls, cabinet and shelf floors, ceiling and hatch inner skins, all using good 5 mm ply.