Going to Thailand in Sept with no idea and 1000 dollars and need help from people who have been there....?

I am going to Thailand in Sept. I have no idea what to expect, I am getting on a plane and heading over there with a grand in my pocket to have some fun! Any advice, probably gonna stay near Bangkok. Things like do I need a visa as a US citizen, what kind of things to do, how much money should I take, for a month, and looking at going to school as an exchange program possibly.