Need help choosing a companion for my Rottie

I own a 11 month old Rottweiler that I adopted at 7 months and he is the sweetest boy despite coming from a household that put him the garage at 8 weeks ( Christmas 2016) and basically forgot about him except for at feeding time, them surrendered him (there loss my gain) So he has some anxiety about being left alone, but we are working it out, I am lucky enough that I can take my dog to work with me. I want to get him a companion as when we go to training class he suddenly develops puppy ADHD and forgets everything he has learned because he is SO ENAMERED with other dogs that he can’t do anything except want to stare, run and jump. We have since moved to private trainings and at a distance puppy/ dog socialization. He is excellent with other dogs (usually he submits) and children, so adult humans he is iffy about and may snap (doesn’t break skin or make physical contact) with if he is Hangry or tired. Never has he done anything to me. my husband or our cat. I want to adopt a 8 moth old American Staffordshire Terrier, I am A) worried that they are both males that there might be some underlining dominance issues when they get older. B) will the terrier go after my cat? Currently the terrier is in foster care with two smaller dogs, 2 bunnies and something else furry that I can’t remember and gets along fine.
Am I worrying to much? can these two breeds live together in Harmony? Any Advice I will take. The Am Staffs foster is almost up so I need to make a decision