I agree with Stede on the sailing courses, you don''t need every course. But do make sure you learn navigation, dead reckoning, and the rules of the road.
I also question why you think you need a 43 foot boat, especially as a single-hander. Everything is bigger, more expensive, harder to fix, etc. There are plenty of smaller world travelers - e.g., Bristol Channel Cutter at 28 feet, Norsea at 27, and a whole host of others, of which I''m sure you''ll be told.
You might back out if the boat ends up too big to handle.
(By the way, my husband & I live and sail on a heavy 37, and when the **** hits the fan, the boat can seem monstrous, just on the edge of too much for two of us. Even though she is a great boat, handles beautifully and will take much more than we can.)