if you are tall the bed has to be fore/aft.
if you are not tall and go sideways- there will always be a climb-over.
building out a van can be daunting- youtube has helpful videos for layout and design.
insulation is crucial for temps and sound
figure my bed is 16" above the floor and 72" wide- if it were higher ( to make better storage underneath, like bikes) then the bed would be narrower as the walls slope in.
fresh, black and grey tanks are central to keep the weight balanced.
mine has a genny where the spare tire would mount...also a propane tank with extra steel around it in case of rear-end
swivel front seats increases your living space- but plan on living outside where there is more space, esp if you don;t have a raised roof like a manufactured class B
rather than an awning a 10x10 popup tent can make for nice shade outside, get screen walls
mine is a pleasure-way lexor TD on a long chev 3500