Lots of good info, I don't have boarders, just my own and a handful of training horses so no advice on the 'hotel' side of it.
A few things I couldn't live without:
-Hot water in the wash rack, we didn't want to spend a fortune with a hot water heater running so we installed an on demand system, all said it ran about $250 for the system. It's great because it doesn't add too much to the utility bill, kick it on 15 minutes before bathing and it's good to go.
-Lights in each stall as well as one on the outside of each stall. Each one has a tie ring and electrical outlet on the front as well. No need for extension cords to clip :)
-I just got an early Christmas from my hubby and it's something I wish I'd have had for years! A heated hose reel - keeps me from draining & walking out hose or carrying buckets, fantastic!
-Good sized stalls, with full walls. We have stallions & I get colts in for training, it's nice that they can't reach one another. Fronts are wood with wire panels so they can all see what's going on though.
Sounds like a great place to set up what you are planning. Good luck and be sure to share pics of the process when you get going!
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.