 If you're going to do this as a DIY project, instead of spending all that time, it might be easier to just put up another coat of drywall over the top of that and call it a day. It might be easier. It might be faster. Most contractors I know of, they do not strip wallpaper off of drywall. They will go through, tear it out, or go over the top of it because it's more cost effective for them to do that