Re: asa school vs buying own 20-30ft and teach self?
Another vote for doing both.
Find a cheap intro sailing course, hopefully one where they will let you rent boats out to practice afterward. You don't necessarily need ASA 101-103 certification ($1200) unless you want to charter - when I started out I found a two-day Red Cross course for about $350 that covered all the same material.
In my opinion, a course is a much better introduction to sailing than learning on your own. Trial and error on the water is not fun. The first day the wind picks up to 20 knots and you didn't reef your sails before leaving the dock and your boat heels so hard the rails hit the water you'll give yourself a heart attack that might cause you to never go out again.
Use their boats to practice for a season while you see how much you like sailing. This will also buy you time to save up for boat, slip, and maintenance budget.
You don't mention who will be sailing with you, but if you are planning to single-hand, lessons will allow you to see how hard that is going to be. If you have someone to sail with in mind, have them take the course with you so you can develop confidence together as a crew.
1987 Pearson 28-2, Deale MD