There are a lot of van conversion videos on YouTube that might provide ideas on the level of effort and sophistication going on out there. Mostly rambling build video series by attractive young couples, but once you sort through the fluff there should be some value.

What price point are you guys thinking? You can buy a new Winnebago Travato (B class camper van in a Ram Promaster body shell) for perhaps $90K. It includes running hot/cold water, kitchen, wet bath, ac, generator, solar, etc. Might put an upper bound on what you can get for a kit conversion and hence limit the available margin.