Thanks for the encouragement, it's appreciated!
I'm going to have to mask off big areas of this for painting, which I've never done before. I have some decent modelling masking tape (instead of the decorator's stuff that pulls plaster off) and I'd thought about using that in conjunction with cling film or something similar. I've also got an old bottle of masking fluid I've never used but I was wary of splashing it all over only to find it gave me extra work to remove or repaint. Any advice you'd give?