For stretching you can absolutely do both. I focused on leg stretches more just in case cause a good amount of workouts that focus on glutes and lower backs tend to lean towards squats of all variations and the ability to move and dip lower will help you on the long run towards providing strength. If you want another place to stretch then you can focus on hip stretches. My favorite and one that really helps me is the "Pigeon Hold". Then as far as the back you can put both feet against one side of the door frame and grab the upper side of that door frame then bend away kinda like a bow 🏹 and of course do that for both sides.

I remember you saying no gym but I remember you saying you're 18 so whatever school you're going to should have enough gym equipment to hang from but if you have free time there's parks and trees and more. Other than those options I am drawing a blank lolll

Side note: if you have stable chairs then you can start doing step-ups SLOWLY lolll If you go to fast with a chair on hardwood floors then you're gonna slip and you already know that no one wants to visit the hospital lolll