Chickens going outside 7-8 weeks

Hello, these are our first chickens and I don’t want to make mistakes. We’ve bought them on March 22nd, I believe they are almost 8 weeks old now, on May 9th. I’ve heard they can stand 35 degrees if they’re fully feathered. I’m no chicken expert. My wife thinks a heating lamp in the coop the first few cold nights is best. So that’s the plan. I’m new to chickens and if I can get by without heat, I think that would be best for them.
We’ve let them outside about a dozen times before in this run. Not overnight, but for a few hours.
We’re in Michigan, zone 6a. Next few nights will be 37, 35, 35, then forties.
I don’t love the idea of running an extension cord to the coop, or a heat lamp in a wood box with pine shavings, but that’s the plan. At least for the first couple nights.
My question is should I bring them inside? Should I do the heat lamp? Or are they fully feathered enough to not need that? I want them acclimated, I don’t intend on using heat next winter if I can help it.
Any advice is appreciated. I’ve looked into chickens a lot online, but I’m no expert. Thank you!