Hi, welcome to the forum from Louisiana. Glad you joined.
If you modify your profile so your general location shows up that can help with a lot of questions. I understand a desire for privacy but something like North or South Alabama should not give too much away.
Chicks develop pretty quickly. Typically they are feathered out by 4 to 5 weeks and can handle freezing temperatures. By 6 weeks maximum. You will probably need to provide heat for a few weeks (don't overheat them) but in Alabama they should easily handle your winters if you order them soon.
You can read different articles that say widely different things. Different members can have widely different opinions. In my opinion there are way too many variables with living animals to be able to believe any specific ratio or any other magic number is accurate for every chicken on the planet. Sometimes 1 boy and 2 girls works out great. Sometimes 1 boy and 20 girls does not. Some all-girl flocks have issues. I think your chances of having a more peaceful happy flock are much better with the 3 girls and no boys. I think that is a great way to go.
Chickens are social animals, they do better if there are more chickens around. If you only have two and one dies then you have a lonely chicken. If you have three and one dies they still have a buddy. I totally agree with Sourland.
I don't know what the coop you ordered looks like. In general I suggest you give them as much room as you reasonably can both in the coop and in the run. I find the more I crowd them the harder I have to work, the more behavioral issues I have to deal with, and the less flexibility I have to deal with things that come up. In Alabama they should be able to be outside pretty much all day every day and not be stuck inside the enclosed portion only due to snow or winter weather. That helps a lot.
Good luck!