Welcome to BYC! It's very wise of you to wait for the coop to be built and to have everything in order before getting the birds, so good job. Bantams can be good layers. I've heard good things about bantam Brahmas, and these are larger than most bantams, so will likely lay reasonable sized eggs. Just a thought. Good luck, and enjoy the website.
Welcome to backyard chickens so glad you joined the flock! Feel free to ask questions and answer questions! Hope you enjoy this site as much as we all do! Make yourself at home!!!
I started with a tiny prefab coop too, and 3 LF pullets. The run was also tiny but I let them free range every day. I've since built a bigger one... remodeling the prefab just proved too... um... not worth it! At least for me. But since you have such a good sized run, now the most important thing to consider is the roost space inside your coop. Chickens need about 12 linear inches per bird to sleep comfortably. If there's two 36" bars, you could technically have enough room for 6 chickens, but 3 or 4 would be better if you don't plan to free range: How Much Room Do Chickens Need? Keeping Chickens Without Free Ranging