I am planning on enrolling in school in Chiang Mai but I understand that the process to get an ED visa can take a few months sometimes.

In the meantime, I need to make sure I am abiding by the proper visa rules for the 30 day visa. I have read in some places online that a person is limited to a total of 3 consecutive 30 day stays within 6 months. But I've read in other sources that that rule no longer applies and a person can have an unlimited amount of back to back visa tourist stamps. Obviously I am not planning to simply stay here on a TV and leave every 30 days, but until I can get the ED visa, I just want to know- what is the actual rule?

I am an American and am in my 30s.

What you are talking about is not a tourist visa stamp. It is a visa exempt entry, that will grant you 15 days at a land border crossing or 30 days at an airport.

Correct, there used to be a rule for border runners, without visas, that you could not stay in Thailand for more than 6 months per year. However that's a few years ago, and this rule does no longer apply.

Ok! That's good to know. I just want to time everything properly as I figure out my educational options.

Note: If you don't have a proper visa, a Land border crossing will give you only 15 Days and arriving by Air will give you 30 Days.