Testing my mongrel cyclonic separator now it's got the reinforcement ring in the trash can. It held up really well, it sucks up the cellulose much more readily than before and with the extra suction it doesn't jam up as often. Since I've only got 1" pipe to actually suck things up and it fits into the 90-degree bend with an adaptor that fits inside the pipe (i.e. restricts the pipe a little) sometimes a slightly larger chunk will cause it to jam, but so far it's doing pretty well. I sucked up about 12" depth in the trash can of assorted scraps the hand shovel left behind , including some small patches of small stones (previously it didn't have enough suction to do anything more than suck them part way up the pipe, only for them to fall back out again).
Now I know where I need to run cables to get the light fixtures sorted out I can make a start on that. I think I'm going to use a couple of junction boxes so I can get one into place without having to worry about moving all the insulation to get at it again to run the next stage of the cable. It's not quite how I'd prefer to do it, but it will work and means I can start making progress more quickly. Now I just need to figure out where the exact center of the room is, so I can cut a hole in the ceiling.