Pretty much anything is possible, if you're determined.
My darkroom is about 6x8 feet in a partially converted bathroom, so we're similar in sq feet. I have a 4x5 enlarger, and do everything from 35mm up to 8x10. Though it's a pretty small space, overall I like the compactness, and it keeps me rigorous about keeping everything in its place. I don't print anything larger than 11x14 on a routine basis, though I could do 16x20's in theory.

Will the space be plumbed? I think the bigest problem you have is accomodating trays and or a sink in the width. Is the hall dead space now, or does it provide access to other rooms that must stay clear?
Tray processing 20x24 will be pretty difficult in a space that narrow, but it's probably workable in drums. Another possibility to save space would be a Nova slot processor.