Agreed with PC. Also, IMO the leghorns have a tendency to be flighty, and can also be on the aggressive side. I've never met a RIR that I liked. Take a look at Henderson's chicken breeds chart. Got kids? If so, you need a couple of Easter Eggers. In my zone 4 climate, my goal is to have a flock of small combed birds: Pea and rose combs for starters. Those 2 combs cross to yield a nice tight little walnut comb. I do have some straight combs, but, again, they cross with the pea/rose which are dominant. I would avoid standard leghorns b/c of their massive floppy combs. Not a good choice IMO for cold climates. I also avoid feather footed birds.You could be much more creative than that. All hens are single comb and the chance of frostbite for them is greater than other combs. Cold hardy breeds should be your primary consideration. Personally not a fan of RIR in a mixed flock as they can have a reputation of being bullies. Leghorns are rather fractious and I've never owned a tame one. Great layers but always moving. Where are you sourcing your chicks from?
More reading for you: Heating pad brooding (IMO the best and most natural way to brood, if you don't have a compliant broody hen.) Fermented feed. Deep litter bedding. You can read about the first 2 topics by clicking on the article links at the bottom of my signature. It's also helpful if you put your general location in your profile. Have you checked out your state's thread yet?