It sounds like you have quite a good grasp of the details of what you are going to do. Sometimes buying/selling things with people you know can present problems. Many friendships have been ruined by financial agreements.
As far as learning to sail her...just do it. Get someone to show you how. Read everything you can get your hands on. It's not rocket science. There are a zillion things you'll need to learn but I sense you'll skate through that. Just don't set off across an ocean before you've been out in crappy weather and know how to deal with nasty seas and high wind. You need practice and experience in what your boat can and can't do.
Are there things the boat needs to go offshore? Radios
, safety gear, watermaker, re-rigging. A boat can cost many thousands to bring up to snuff. Where will you dock it? How much will that cost? Boats require continual maintenance. Something is always breaking. How is the engine? Make up an Excel spreadsheet of projected expenses then add about 40% to see if you can afford it. Personally, I would never finance a boat and think it is a very bad thing for which to be in debt.