Wallpapering - easy peazy, done that loads of times.
However, this time the underlying walls are a bit of mess. Most (but no all) of the paint on the plaster came off with the previous paper, and the plaster type varies too, mostly pink carlite, a few patches of dark grey thistle and some white one coat stuff. Previous paper was painted blown vinyl, so no issues with underlying background showing trough. Going up this time is a very light coloured printed paper - what's the chance of the patchy background showing through if I don't give it a coat of paint?
(Its not the time to paint that's the problem, its that paint over glue residue is a hideous mess and I like to give the walls a good clean first if painting, but that is hard work!)