someone told me if i tried to start all those activities at the same time id burn out quickly. my plan is to lose fat,gain muscle and learn to fight
The cardio you can start now, and it’ll probably help a great deal w/ your Muy Thai.
How active/athletic are you now?
You may want to give your body a good couple of months of weight training before introducing the Thai boxing, which will be an entire workout regimen in and of itself.
After a while - and depending on how serious you get into this - you may decide to shift the focus of your “gym” training all together in order to improve functional muscle and strength for the boxing.
There are vast differences in the way weightlifters train to enter a physique contest vs. something like MMA or kickboxing.