I have a floor to ceiling cabinet in my bathroom that I put together in the bathroom and made a little shorter than the 8 foot floor to ceiling height and covered the gap with crown molding. This is smaller than yours, however, which would affect standing it up. I'd make yours in top and bottom separate boxes. You could hide the joint with the face frame.

I also like to make the base separately unless I can't due to the design. It is easier to set and level a separate base. I don't think I would use pull out trays. Shelves should work fine and could be adjustable. I wonder if there is space to pull the tray out unless the room is big.