Re: asa school vs buying own 20-30ft and teach self?
In my case I did a bit of both, doing the ASA 101, 103, 104 and 105 courses over a couple of years while sailing a 16ft dinghy on lakes and the bay. The later, more advanced courses will mean a lot more if you have been doing some sailing in between.
What I don't like the idea of is these packages where you do, say, 101 and 103 in a week. I prefer the idea of spacing them out a bit, and each one should take a week (or two weekends). You need to maximise time on the water, not minimise it.
I still look back on those courses as some of the best times I've had. Rather than a chore, they made pretty good vacations - taking a week off work and sailing beats working, any day.