Identifying plaster type and how to best remove wallpaper and prepare for painting?
I would say that the best way to get a nice smooth surface to the entire wall (after removing the wallpaper, naturally) would be to plaster skim-coat the entire surface. This type of job requires some skill and a novice would benefit from practice. Another (less optimal) option would be to sand it as smooth as you can and touch up the roughest areas with plaster. Pros use bright lights at an oblique angle to highlight uneven areas, for situations where the flattest/smoothest surface is important. In this situation, either method calls for a complete prime coat prior to paint.
For removing the wallpaper, there are specialty tools and products to make it easier, e.g. scoring tools to perforate the paper, chemicals to help loosen the glue, sprayers to soak the paper, special scrapers, etc.
Since you obviously have internet access, I recommend that you watch some video tutorials for skim coat, plaster repair, and wallpaper removal. This will help you understand the options you have, the steps involved and the equipment and materials needed to do it right.
P.S.- the type of plaster that you have now is not terribly important...