Take a walk through with the home inspector and see what he says. If you are still interested in the house, find a good general contractor (that you trust) and take him on a walk through. The contractor should be able to give you a good estimate on what it will cost to fix any issues, he may also give you some price breaks if you are willing to let him handle all the work.
Just make sure you are comfortable with the contractor before you ask them to go on the walk through, they might be upset if they take time to walk through with you and then you find a new contractor to do the work. Keep in mind, however, that if the contractor starts work and does a sub-par job, you can always fire him and find a new contractor.
If wallpaper was painted over you could tell pretty easily by pulling on some of the peeling paint and breaking the paint chips. Wear a respirator mask while doing this, however, as often times flaking paint is a potential indicator of lead based paint. If the chips contain paper, then you're right, it's wallpaper with paint over it. If it's just paint, then be more careful - get the chips tested for lead.
Given the wide spread flaking, it is likely that the wall simply wasn't properly primed. An improperly treated wall when painted over will eventually lose adhesion with the paint and it'll flake away like you're seeing. If they applied paint directly to wall paper w/o priming, I think the same is true.
That 2nd picture DOES remind me of wallpaper... I've scrubbed far too much backing off the walls and that looks similar.
The grey subsurface is, I think, a kind of stucco mix that was often used to even up walls where lathe and plaster was replaced with the older style 2x4 drywall panels. It's nasty, gritty, dusty, unpleasant stuff, tougher than joint compound/plaster to work with because of it's tendency to crack and break rather catastrophically. When I run into that stuff in my rentals my approach is, "IF I have to touch it at all, it's ALL coming down." Plus with wallpaper I swear gutting is easier than stripping.
Now around the vent pipe, that looks like moisture damage. The bubbling around the pipe suggest water leakage. Is that a "finished" ceiling - ie - thats the roof on the other side of that wall w/ the pipe? If so, make sure it's properly sealed and replace at least that area of ceiling.
Picture #5 seems to confirm this - someone touched it, and patched it badly.
Best Answer
Your 1st picture shows an issue where you have a layer of paint which is not well adhered to the surface underneath (and probably more layers painted on top of that).
This is like putting a piece of scotch-tape onto a dusty surface and expecting it to stick.
More and more layers of paint will never fix this.
You'd need to strip/scrape/peel all of the old paint off until you get back down to something solid and start the paint journey over again from scratch.
While doing this you'll probably also find what's under that crack in the 2nd picture - there's likely still movement on each side of the crack, but it might be possible to manage this once you know what's under there...