You do not need to be fit to start. Camps that run beginner classes will meet you where you are and scale the work. That said, camp days are physical, and a base of fitness makes the first week far more enjoyable.
Two sessions a day is common, and the heat adds to it. Your legs and shins take the most early load. If you have only trained lightly, plan to ease in, take the rest day, and hydrate well.
If you want a running start, a US coach can cover the basics and your conditioning at home. Learn stance and strikes near home, then arrive ready to train, not to start from zero.
Compare verified camps, or prep with a US coach before you fly.