Thanks for all the comments. Don't be too anxious as I am a slow worker!
The latest stage - with half the crenelations done. Obviously needs a bit of filler. I probably should have been a bit neater with the 22.5 deg cuts but nothing milliput can't fix.

The idea was to have something pretty modular that can also be expanded in the future. With the modifications I am making there is probably a dozen different ways of laying out a castle plus I can use it for a fortified manor house, chapel, hall, church or watchtower.