Hello and welcome to BYC and the Chicken obsession. I'm glad you decided to join us here.
Don't worry too much about making a mistake. It happens to everyone. Just do your research, ask questions here if you have specific ones, and everything will be fine.
Hi Emily, congrats on the new home and upcoming addition to your family! I'd caution you about putting Polish in with other breeds...those feathery heads can be a target to other breeds (that was my experience anyway).
Welcome Emily. Leghorns are not the friendliest breed. ( Good layers though) Spend time with your chicks and let them get used to you being the hero/ treat giver. That helps make them friendly. I got mine at 6 weeks and gave them small amounts of scrambled eggs to get them used to me.That really helps when it comes time to inspect for disease/ parasites or possible injuries They still like to eat out of my hands at 1 1/2 years old. Talk to them and remember they only peck they have no teeth. Good luck