If you want to use your own boat then you'll need somewhere where you can launch/recover at any state of the tide.
And offers courses all year round.
Think your nearest one is probably going to be Falmouth, in addition to being able to launch at all states from a concrete slip you're protected from the weather in the Fal.
No idea how good/bad they are though & you'll need to speak to them about using your own boat.
http://www.falmouthschoolofsailing.c...ndling-course/
ETA Stithians Lake also comes up on your list, no issues with tides but reservoirs can be funny about power boats other than those provided for fishermen or used as safety boats by the sailing clubs that operate on them. Again, you'd need to give them a call.