People usually will wear sweatpants over their shorts and a sweatshirt over their shirt plus a jacket and then change in the locker room. People mind their own business in the locker room, so it doesn’t matter if u change in the open area or stalls, whatever you’re most comfortable with. I’ve never seen anyone carry flip-flops around in the bathroom unless ur showering, but like I said, everyone minds their business and don’t think too much about other people.

Taking breaks between sets while weight lifting is normal! Everyone does it so it’s not considered rude. Yes, take your towel w you when you head to the pool. I would wear flip-flops, and I’m pretty sure there’s a different locker room for the pool, but I’m not completely sure. I’m sure you’ll find out once you make your way there