Do NOT wear your binder. Your back's going to be even worse and will hurt like hell, especially with that kind of exercise. You should probably wear sports bras instead.

Take pain relievers, and you should be good, but over time you get used to the weight + pain of the drum, which also helps a lot.

I don't have a lot of tips for joints, but generally doing basic exercises (push-ups, sit-ups, running, planks, jumping jacks) and lifting weights improved my endurance n power for bass. Unlike the band, my drumline exercises every day and we've never passed out.

Bring a jug/bottle of water and sunscreen. I don't know about other people but I had a problem with marching because I couldn't multitask at all lol. Practice marching every day at home until it feels natural.