Painting over Wallpaper
I've just painted the whole interior of a house that was wall to wall wallpaper. Any pieces that were sticking up I just used PVA glue to glue it back down. Wallpaper was pretty old, early 70's, oranges, browns yuck.
I used acrylic top coat, one was enough on most rooms. One tip though. If you undercoat with acrylic undercoat and the wallpaper underneath is either dark or has big orange flowers on it the patterns/colour will bleed through even after you've put two to three top coats of acrylic on it.
I sugar soaped all the walls first, the wallpaper wasn't washable, but that's no problem just don't soak it to death. I used a squegee mop and just mopped the walls. You don't need to rinse it off.
Then I used oil based flat white paint as an undercoat. I already had some of this that I was using as a ceiling white. It's really good if the ceilings are yellow from smokers because if they were and even if you clean the ceilings, if you use acrylic ceiling white the stains will bleed through in some places. Also good if your new tenants happen to be smokers, you won't have yellow ceilings when you get new tenants in.
So, use oil based flat white paint over everything. Then paint your acrylic top coats over that the next day. Two coats is probably better, but you should be able to get away with one.
Mine came out really good, some of the old wallpaper was embossed so that gave a really nice effect to the walls.
Good Luck