My wife and I have basically gelled on a layout - this is based the line drawings of the Thomas 14-window RE bus, so will obviously require tweaking to match whatever we end up getting, but this is what we've come up with:
From the front (left):
The Driving Space:
Driver side: Driver's seat and a 'driving dinette', with four sets of seatbelts and carseat anchors where the kids will sit while we drive, and where I will work when we're parked. Seating for six should hopefully cover us off forever, because if I have more than four children I will go insane.
Passenger side: navigator's chair followed by a 'hanging locker' for jackets and boots and shoes and such.
Kid's Bunks and Heads
Driver side: Bathroom with Nature's Head Composting Toilet (not gonna argue about it :P), 32"x24" tub and counter.
Passenger side: Two bunks, 28" wide at the aft (pillow) end, 23 (if I remember right) at the forward (foot) end.
Driver side: Kitchen counter with sink and 24" propane cooktop - we did just fine on the boat with no oven, and we figure the same here. I'll be building the cabinetry with an 'insert' there so we can swap a full stove in there if we change our minds.
Passenger side: Closet, then (24") fridge, then pantry space. Weeee.
Seating and Living
Seating and living space is basically just a giant couch/settee, with a foldable table, and some empty wall space for a Christmas tree and strewn about toys.
Mommy-Daddy Sleepy Space
At the back is a king bed up on the engine cover, which will also double as a playspace.
I'll update this with a link to the conversion post once we finally get a damn bus - which will probably be in the spring.