I'm an ESL teacher and actually pretty high up the totem pole when it comes to experience and pay and such. Even so, I can tell you that you'll want to make sure you already own anything you'll need before starting to teach. This includes the boat, gear
for a few months provisions, and anything else you may want.
It's an enjoyable profession and it's really not difficult. And if you decide to locate to the Caribbean
or Central America
it can be really fun. You can support yourself living in the location, but don't expect an income
that will allow you to improve your situation (thus the have everything first comment).
I wouldn't invest too much money
in training as most of the courses don't really teach anything that's not common sense and the pay doesn't increase much with more education.
Now, if I can only find a decent paying job for a few years to buy my boat...I'm right behind ya.