As above- stip down to your pants and make a sauna of the room. Spiked roller, find a decent scraper that you find comfortable- you are going to be holding it for a while! I find that scrapers are a bit like fountain pens- they sort of become worn/ matched to you. When I moved in to this place every wall and every ceiling was covered with layers of paper, polystyrene, woodchip and gloss paint, in a multitude of configurations. All on top of lath and plaster.
The electrics tripped more than a couple of times, I think due to the high humidity in the room.