Welcome to the coop! I use the Forums and Articles tabs at the top of the page to do research. You can get lost for hours. It's nice to know you are minutes away from getting help with questions and emergencies! I have two Dark Brahmas; they stick together and will stand up just fine with other breeds. I have several types. Beautiful regal ladies!
Welcome to BYC! thanks for joining us. I live in a swampy area I don't keep any chickens with feathered legs or feet. The mud in our area can last for months occasionally. They look like heck with the feathers all junked up. We learned the hard way many years ago, I agree with @janiedoe. Good luck with your new birds.
I personally don't think it would be an issue to add a Brahma so long as they are introduced properly. Whether or not the mud is an issue depends on exactly how bad it is. I have thick clay soil in my area, and even my birds (who have no feathers on their legs) can get very weighed down if they walk in the wrong spot for too long. They have wood chips and old leaves around their run to prevent that from happening, so that might be an option for you if you're concerned about mud. Best of luck!