I am going to advise to start letting them out much earlier, as they are learning about their environment, and by keeping them safe, they will not know anything about the great beyond.
As you have buff orpingtons I would not worry about them roosting in the trees, they tend not to fly high. Chickens are highly habitual, and so if they are roosting in the coop, they tend to keep that pattern.
However, I strongly recommend having a coop/run set up. It is not healthy in my opinion to lock birds into a coop for days on end. And there will be times when you are away. In my opinion, there should be a run big enough to leave the birds in 24/7 if needed. Now you can always let them out, but sometimes you will need to keep them contained. They should have the choice about being outside or inside as needed. Being outside is important for even chicks, even if only for a limited time each day.
Predators are a real problem, and can wipe you out. They will treat your set up like a fast food restaurant and come back and come back until they are gone. When you get hit, you need to be able to lock them up, for several days so that the predator moves on. EVERYTHING loves to eat chickens. Wishing and hoping they won't bother you is not real practical.
Mrs K