It's already been said, but a plastering course will mean endless work, You can never get a plaster, my mate had a bloke do his lounge and was supposed to come and do the rest of the house £££, he ended up having 5 plasters do different rooms as he could never get them to turn up when they said they would.

Loads of people I know really struggle to find plasterers so if you get known as a decent reliable one you'll make a mint.

Plus you can be self employed so no boss, and you own working hours and low overheads.