At six weeks old in North Carolina this time of year, move them to the coop. They are ready. You don’t mention how cold the nights are but they are almost certainly past being ready for that too. I doubt you are seeing anything close to freezing. I’ve had chicks less than six weeks old spend the night in an unheated coop with the lows in the mid 20’s.
If you turn your chicks loose in the back yard you may or may not have problem catching them. If you have been handling them a lot and they come to you when you have food, it probably won’t be too bad, maybe even really easy. If they have not been handled a lot, yes, it could involve a lot of chasing. They are pretty quick, also fast, and can get in some hard to reach places.
I regularly let my 5 week olds range with the main flock in a large area enclosed by electric netting. There are plenty of hawks and even an eagle around. It hasn’t been a problem for me but some people have really bad problems with birds of prey. Any time they are outside they are at risk, but usually it is not nearly as bad as you imagine. If you are present you reduce that risk quite a bit but it will always be there. I don’t know your situation on how bad the risk really is or your risk tolerance, I can’t tell you what to do.
You might consider turning a baby play pen or something similar up-side-down and letting them play outside under that. We all have to find our own way,
Good luck!