The only advice that I can give regarding the layout is as follows;
Regardless of how an OEM sets up their interiors, frames, drivetrains, etc.... When you undertake a project with this scope, you will end up changing things, even several times. For example, I wanted a vehicle with a trimmed out interior and a headliner. I thought it would save time during the interior build. Problem is... the headliner interfers with installing an exhaust fan, and the stock interior panels get in the way of the cargo area. Conversely, a stripped down cargo van will need all sorts of bits and pieces, whether sourced OEM parts, or fabbed yourself. These issues are not brand specific. I've spent a lot of money on vehicles in my 25 years of driving, but it was not until I got my Ford Van that I based my decisions on what was cost effective. Previously, it was based on cool factor, brand loyalty, or uniquenessity (new word!:costumed-smiley-007 )
The burning questions are... Where do you want to spend your money? How much are aesthetics worth? Do you have the time, Resources, money and energy to go custom? The Ford E-series platform has proven and reliable aftermarket support, ready to bolt on. Chevy is still catching up. Custom is always an option, abeit more expensive. Of course this all depends on your build needs. Mine were; daily driver capable, carry 5 passengers, all weather dependability, range, aftermarket support, maximize OEM parts used to ease replacement/sourcing issues...
In the end, I want to spend my money on fuel to get us to the places we want to go. In the past, it would have been on the coolest, most unique vehicle, regardless of ease or economics. I am beyond that now, but feel that I am making the best decision given all the above. And Chris over at UJOR makes a mean product, and his customer support is second to none! Hard to go wrong there...
Anyway... off my soap box. Good luck in your endeavours! Hope I can help along the way.
Brad