Yeah, his home is his office.
make sure you build your desk so that you can pull your legs under the top and belly up.
Think about rebuilding the bathroom wall "theatrical flat" style (sorry, it's all I know at this point) 2x4's turned sideways. Thin yet strong. Insulate, insulate, insulate!
Don't worry about the quality of the plumbing for a while. Figure out where you want things first then worry about service.
how is the quest for a new mechanism going?
Luan, applied to adequate framing can be your ally. Don't be so quick to pooh-pooh it.