You may be having trouble getting the steam to penetrate the wall paper's plastic film covering. I haven't done a lot of that work but most of the time there's a first layer of plastic you have to peel off. Then you soak the paper -15-20 seconds per 12" square. Start at the top and let the water work itself down the wall.
You could also try the old score and dif wall paper remover. Some people love the stuff some hate it. I've always steamed so I can't say either way.
As for primer I wouldn't mix anything into it. It dries fast anyway. I guess if I wasn't going to strip the walls I would pop bubbles. Spackle or even float them all out. Sand, prime, paint.