Well done David. I don’t think anyone needs to add any criticism, you seem to have covered that yourself, and that’s a good thing to do when you are starting off.
It’s worth spending an hour in a room measuring everything if it will save you an afternoon of messing about. Good things to have are a pinch rod for measuring heights to ceiling, inside widths of alcoves, a framing square to check corners, a good spirit level to check walls for plumb, rises and falls in the floor and ceiling.

Doing the best I can with what I've got