I recommend working on your cardio before you joining any gym.
I trained as a boxer for a few years, took some time off went back to the gym thinking I was in good enough shape and got embarrassed badly.
Beginners dont realize the amount of cardio you use and need while learning any kind of striking. Prepare to get your ass kicked, but that is a good thing.
I have never trained in Mauy Tai but I can imagine it is a lot more tiring than just plain ol' boxing.
Congratulations you won!