The current plaster sounds pretty ropey and is probably being held up by wallpaper, so removal & disposal of any old plaster that needs to come down, replacement plasterboard where necessary, or patching up is possible, then all skimmed for a smooth plaster finish. The room is roughly 2m x 3m although I imagine any quoting parties will want to see the room and state of the current walls first.
Andy was always on time, from quoting through to finishing the jobs I paid him to do. Very professional in his approach. Wouldn't hesitate to ask him to do other jobs