Hello everyone! We are first timers too! We have 8 chicks, their ages range from 7 weeks to 9 weeks (1 silkie, 1 brown leghorn, 2 easter eggers, 2 barred rocks, 1 black sexlink, 1 lavender orpington). They have been outside for a week now and I thought I'd share our journey to moving them outside from the brooder, in case it is helpful to anyone looking to do the same in the coming weeks.
We got most of the chicks at 6 days of age. They were inside with a heat lamp for the first 3-4 weeks. I kept the heat lamp on one side of the brooder and adjusted the height based on the chicks behavior. If they huddled under the lamp I moved it down, if they didn't seem to be using it, I moved it up. I did not use a thermometer. I tried the first day and they knocked it over and jumped and pooped on it.
At 3-5 weeks of age we moved them to the un-heated garage with a heat lamp. (It was February, we live in North Carolina). The lows were in the mid-twenties. They were fine. When they were ranging in age from 5-7 weeks, we turned the heat lamp off during the day and turned it on at night for two days. Then, we turned it off completely for 3 days, but kept them in the garage. Then we moved them outside, they were ranging in age from 6-8 weeks at that time. They have done beautifully. (During the heat lamp weaning in the garage they spent the warmer days outside in the coop until nightfall)
I was concerned about them sleeping on the ground of the coop, rather than up on the roosting bars, where they would be MUCH warmer. (Our coop has hardware cloth on the bottom half, but plywood on the top half, so when they roost, they have a wind break.) I went out to check them after nightfall the first night and they were huddled on the floor, looking rather cold. I placed each one on the roosting bar and went back out to check an hour later. They were still on the bars. I checked a few hours after that, and they were still on the bars. The second night I had to place them on the bars again. The third night, I went out to put them on the roosting bars and they had already done it themselves! I was THRILLED. Now, they start making their way up the ramp each night as it starts to get dark. Once it is dark, chickens stay put.
Good luck with the transition!