The biggest concern with having only one bathroom in the house is the size of said bathroom. Ours was no picnic. Let's just say that I could scrape my knee on the vanity if I was doing a number two. Subtle, I know. So we had to fix this problem before anything else major in the house. Here's some before pictures.
I drew up a number of plans and went to work. The plan was to knock out the front wall into the guest room and steal about 20" of space. This would involve framing out a new wall, moving some plumbing, drywall everywhere, framing a new bathroom closet, tiling the floor, and adding hardwood to the additional floor that was in the hallway (the corner of the hall would become a right angle instead of a curve). While I have done all of this in some capacity before, there was a lot of learning as we went on. I also learned my wife is a demo machine!
One noted takeaway we got from the demo process is that plaster is the worst! It's heavy, hard as concrete, and if you end up with corners where they use metal mesh to hold it up, good luck with that! If you can hire out the demo and drywall mudding/sanding later, I would highly recommend spending the money and avoiding the pain in the ass!