This will be interesting to follow. I'm doing pretty well the same thing in the next year or so when I retire. I'm looking at the high roof transit or sprinter in their longest heaviest forms with 4x4 conversion. I plan to go with the diesel and a webasto heat system. I will figure a way to fit a decent oven in there, not a cooktop. I know the transit is touted as nicer handling than the sprinter but the sprinter at this time still offers the most space.
Here is a Transit van build you may get some good ideas from.
Transit buildOne thing I have been thinking of doing in my build is using a couple rollaway tool boxes less the castor wheels for cabinets. Nice steel construction about 16-18 inches deep. Roller bearing door glides and lockable. Various drawer size combinations available.
