I got the first coat on the hallway and it looks much better than that old nasty wallpaper. Of course, it just makes the ugly carpet look even uglier...but here's the before and after.
I have shut the door on the bathroom problem, literally, for the day. However, our friend Paul (a.k.a. Wonder Dude) recommended using Kilz primer on it and then skim coating as necessary. This is a much easier solution than what I was envisioning. Once again, Paul has saved me from unnecessary and much more difficult work with a simple solution. Hooray Paul!