A few reasons, budget is big one, second one is my design is changing as I build so with the windows everything would be set once that hole is cut so I've left enough space and I'll build around it for the time being. I had planned 5 windows, 2 over my bed, 1 big one in the kitchen, 1 side door and 1 rear seating. However after I got my bed up there I didnt think about the bed headboard so I might only have 1 window there.
I will be adding it as some point but it might now be reduced due to the weight, I was planned 25mm celotex but to cover the entire van its near 60kg. So I might just vapour barrier then add my internal wall covering. I'm going to use the van over the winter without and then make my mind up next year.
Shower will be secured into the van internal framing but its just a place holder now for idea/looks. Again this will be something next year due to budget
It's normally worth bearing in mind that should you have to sell the van due to finance difficulties or for some other
compelling reason that you're going to realise a decent sale price. Not to overcapitalize too much as it were. Of course
you have to do things primarily to suit your own needs.
Ebay always has plenty of half built vans for sale with thousands spent on top spec. electricals, appliances graphics LoL
and precious little on (crap) insulation or body corrosion, some definitely take a hit.
Don't forget to drill a lot of holes in those bed boards, you'll get condensation otherwise, & makes the van a little lighter!
You could PVA glue-in small wood block triangles at those frame screwed junctions, where you require more strength, costs
nothing.
If you're intending to so called stealth camp, then more windows makes for more conspicuousness.
I note that where you are spanning the full width of the van you've fitted some angled braces presumably to save weight?
If you find the surface too springy, a method of stiffening those full width joists is to screw fix at say100mm crs. some
25 mm x 2mm galv. steel straps the full length on the underside, will add a lot of strength and you'll probably be able
to remove the angled braces making the space more usable, but test first!