I've been wondering about Thay for a long time. After my Chessenta campaign is complete, I thought about starting a campaign in Thay. I'm also wondering why it's society hasn't collapsed yet. And I like to find out.
I'd start with checking out the Thay entry in the FR Wiki. https://forgottenrealms.fandom.com/wiki/Thay. It might actually answer your questions. That said, I would actually suggest you get the 2E Spellbound box set or 3E Unapproachable East instead. Almost everything in FR6 is reproduced and expanded upon in each of the latter two supplements which add more info on nearby nations as well. That said, I'm sure there are some nuggets that didn't move forward into the latter two.