Budget on the boat is an interesting thing.. if you are unsure how it will work out, then buy the ubiquetous but difficult to find - well founded boat - however, should you decide you like it - budget for the boat and to spend 50 to 100% of the purchace price making it your home to your standards and self sufficiency.

As for first aid.. the paramedic reference is good. I am an EX paramedic with 14 years in the 'trade' - most ambulance services offer first aid courses - FAR better than any 1 day rya course - avoid st johns like the plague.

If you can get a few together, ring your local ambulance service training department and tell them what you want - forget certificates - just advise them of your intentions and let them plan a course for you.
Buy - Ship Captains Medical guide too.
Also, agree on 'if it dont work out - ditch the bird lol)