Lots of wisdom imparted here. What you start off with may or may not be what you wind up sticking with, for any number of reasons. Finding a breed, or more precisely, a line of a breed, that fares well in your environs is top of the list, so you aren't constantly tweaking everything to keep them alive and healthy. Figuring out which has the temperament you are most comfortable with would be second, taking into consideration whether you will have family members helping/interacting with them regularly. Example: I had a small flock of Black Leghorns that were nice, but I really wanted Dark Browns, and DH was distressed by their responsiveness to everything that happened around them; since they were not what I really wanted and he was troubled by them, I sold them. Cochins, he adores, so I have a lot of Cochins, and a trio of Rhode Island Reds. I have a couple of Naked Neck hens living with the largest flock of Cochins, and we noticed last year they are a thousand times better at chasing and catching bugs, grasshoppers especially, than Cochins, so this year I added more Naked Necks - mostly to serve the purpose of grasshopper control, but also because I adore their little Dr. Seuss-looking chicks
You will find the 1, 2, or 3 breeds you are happiest with, possibly after some trial and error. Having multiple coops and runs will always serve you well. Here, we let each group out to free range separately so there is no chance of crossbreeding, rest of the time they have large runs so there is no crowding.