How you are going to fit out your van depends on how you will use it:
cold and/or hot weather
long and/or short trips
campsites with hookups and/or boondocking
you only and/or other people
The other thing is to use the RVan during the process so the design can evolve to suit your particular needs.
I did my own "outfitting" starting with a used high top conversion van that already had an electrical system and a top mounted, 120V heater/AC added on.
my RVan Like you, I wanted a modular, lighter weight system. I got rid of the bed entirely and sleep in the recliner (as I do at home). I really like the plastic carts I have in mine. I have the same ones at home so to load up for trips I just pull the drawer and take it into the van. I found some smaller cargo nets to use instead of big clunky wood/particle board overhead cabinets. I love the cargo nets, but for more organization got clear plastic shopping bags behind the cargo net.
One sleeping system I was looking at for my DH for in his little tear drop is called a
Froli system but my DH went with a "6-Inch Memory Foam Tri-fold Mattress" that folds into a chair.
I too suggest
looking at van conversions at this site