Kinda hard to see in the pics but this sounds like a LOT of cracking. I might suggest having an expert see why so many. Please remember he is there looking at it and I am not. But I would question him about the cracks returning, to skim with joint compound will cover them but joint compound applied thin like a skim coat has no strength. At the least I would apply PAPER tape over the cracks then feather them out sand prime and paint. And as said no PVA use something like Zinzer 123.