I'd either keep the 4x5 (sell the 5x7; film's too much of a PITA to get), or get a top line digital DLSR.

Darkroom's going to be the big space consumer (even if it's a portable style as storage will be needed), so a 'Blad isn't going to save much room. Removing the darkroom by getting a digital will save you heaps of room.

You will, however, need a big shower. Using digital will leave you feeling very, very dirty...