Removal of wall paper paste

Hello Don't even attempt to paint the wall with any residue on it. Wait until it's dry and sand it down. We use a festool orbital sander with a dust extractor to ensure you have a perfectly smooth surface but sand paper is good enough though. Once that's been done seal it with zinsser gardz and then it will be ready for your 2-3 coats of emulsion. If you're going to wallpaper it, sand again once dry and line it ready for paper. Lining walls is done so the wallpaper has an equal drying time across the wall not primary for imperfections.

The wall needs sanding.

Fine to wallpaper over that. But if you are going to paint you do need to be careful because paint will react with any paste residue left behind. If the walls were sticky when damp then it is likely there is still residue there. To give yourself a good base and seal the walls to prevent problems you can buy a product by Zinsser called Gardz - you can get this from Gibbs & Dandy or search online. This is a clear coating that locks in the paste and evens the surface. It does add to the cost but is better than needing to sand the walls down after you paint and the paint cracks. Good luck.