I am moving back into my townhouse after it was rented out for 16 years. Ugh! They stripped off the wallpaper on some wall and did not do it correctly then painted over it. I see all kinds of ridges, bumps etc. If I sand it down (maybe) can I then paint over it again and it look right?

Also, this townhouse is over 20 years old when they wallpapered right over wall board with only the seams of the wall board are skimmed with joint compound. I have started sanding another room and after I remove all the old wallpaper paste to do venetian plaster to hide all the wallboard beneath. However, this is a small bathroom and the Valspar brochure said it can not be used in moist areas. But, in a show they applied VP to the backsplash in a kitchen. Any advice on how to deal with the wallboard delimmas?

Where they removed the wall paper and did not get the glue off and painted anyway.
Your in for a lot of work. Once the glue dries even when its not painted is a difficult chore. I suggest you get a orbital sander, with some 220 grit sandpaper (lot of it) and carefully sand the wall high spots until its smooth. You can if your fairly good use a spackle compound and skim-coat the walls but you need to sand anyway to roughen up the walls so it will stick.
Its a diry job but can be done.

As far as the wallpaper over the walls could you please be more specific on your question.
Or perhaps someone else understands and can answer.

The bathroom had wallpaper 20 years old. I was able to pull it down without any problem (it was almost rotten) and it left a thick layer of paste behind. I have started sanding with a palm sander the paste away and this seems to be working. I then will wipe the wall board down with vinger water or another solvent to remove the remaining paste.

I will be left with wallboard that at the seams and over the nail head (they did not use drywall screws when built??) is covered with a skim coat. I will then prim with Kilz. This is why I wanted to do venetian plaster. Because, I am afraid you will be able to see the imperfections with just paint and I don't want to apply wall paper to the room. Is there a venetian plaster or other product that a novice can use to cover the bathroom walls?

After you have finished the sanding, it would be good to put a thin layer or two of joint compound over the rough areas. When this is dry, prime with a good coat of PVA drywall primer.

I believe you can put venetian plaster over PVA primer, but check the product specs first. Some venetians may require their own special primers as preparation. Good luck!

I ended up doing a skip trowel texture on the wall and it turned out very well. In the other room I decided to recover with a thick wallpaper that complimented my color palette and design taste. Finally, in the last room I used the texture treatment again in a wisk broom style below the chair rail and a sand paint above. I learned a lot using these techniques and am very pleased with the outcome.