That's close to what I do. At five weeks in your weather they do not need additional heat. My brooder is in the coop with the adults. At five weeks I open the brooder door after the adults are outside and leave it up to them.
Each brood is unique. With some they go outside pretty quickly. I have over 2,000 square feet outside so plenty of room. Some broods wait about three days before they head outside. Eventually they start going out first thing in the morning and stay out all day. I have food and water both in the coop and outside. It sounds like you don't have any adults. I'd let your chicks set the pace for going outside.
Since they have been housed in the coop for three weeks they should see it as home. Hopefully they will return there to sleep at night. My main coop as at ground level and that is what happens. My grow-out coop is elevated. Instead of them taking themselves to bed in there the first nights I let them out they tend to sleep under the pop door. You may need to put them to bed inside for a while before they learn. So, yes, be out there at dusk and do what you need to.
I've had broody hens wean their chicks at 3 weeks of age a couple of times. Those chicks were able to make it on their own but the hen has spent those three weeks training them how. You may be amazed at how well instinct takes over and how well they do.
Chicks that age are more vulnerable to predators than they will be when they grow larger. Snakes or hawks might be more dangerous. I have really good luck with that but some people have real problems. We all have different predator pressures.
Good luck!
