Hey Kurt! And welcome! Have you tried searching YouTube for Van Builds or do a #vanbuilds on YouTube? Lots of info out there. If I think of something more specific, I’ll try to remember to come back and post.
I have some helpful advice. Everything in a van camper is similar to a travel trailer or motorhome. Those are mostly manufactured in Elkhart Indiana. So I would search suppliers in that area for parts. They should come with direction and if you locate an RV parts supply company, you should find all the specialty parts you will have to have to build out.
Also Marine Stores and catalogs, Blue Sea Systems is a good place for electrical parts, panels, reference charts for wire gauge amp/length run. Good tech line.