Thanks for that info, neil.
slownsteady, I think I'm going to do a little of both. I have a friend who is pretty handy. I have some knowledge on how to do things, unfortunately my physical skills do not match what is in my head. I also plan to ask my plumber some questions and see how much he would charge to do things. I am still hoping to do as much as I can by myself --like taking down the wall panels, taking out old fixtures, removing old floor, installing subfloor, installing moisture barrier, installing vanity, installing vinyl sheet (which I've done before), and installing the toilet (also something I've done before). I may need help with any heavy lifting, so that is where my friend comes in. I've put up wall panels before, and I can do painting if any is needed.
I was going to say I would ask my brother for help, but he's even worse at DIY stuff than I am. LOL. Although, he might be ok at some demo just from his sheer weight. I'll have him lean on stuff.

He already put a big hole in one of the walls accidentally.
In terms of progress, I talked it over with my mother and she already bought the Oatey washer box and the valves. She said that we should do the work in spring when it won't be too hot or too cold. It's the first time she's actually semi-committed to a timeline. There's a surplus store that should have sheet vinyl-- since it is a rectangular room, it will hopefully be easier than doing the floor in my bathroom.
The thing I'm most concerned about is getting the tub/shower installed properly. So I'll have to do a lot of research on that.
I'm just babbling away... and my cats have captured a rat....