I like this graph.
I'd have one 400w sodium bulb with as much height in the cab as I could get. Carbon filter and fan is a must. I'd get a 5 or 6 inch fan.
Air cooled hoods are great if you can afford them but you could run a 400w in there without except maybe in midsummer. An air cooled hood would be best if you want to run a 600 in there.
Because you'd have extra height you could run stretchier strains without too much hassle.
If you want you can always add another deck later.
That's just what I'd do.
If you do want to do the double up-
Do consider a scrog- you could make a frame like you say so you can lift out each level as one unit. The screen would be ideal for keeping a nice even canopy- which will be critical.
Or you could have a SOG- make little plants to flower small.
You could still use a variety of different genetics, as long as you are prepared to do the appropriate training.
You would need to fit in the fan and filter- and a couple (min) of circulator fans and conduit for air cooled hoods. It's going to get cramped in there.