While I myself am not (currently) poly, I do a few friends who are. From my experiences and those of said friends the hardest part of balancing the relationships is exactly that. Balance. I only ever went from one to two as I know myself well enough to know that if I expanded any further than that I’d start slipping on keeping up with people. My closest friend who is poly has 3, sometimes 4 people, and those people are with others who are not the same group. It’s kind of a web of people.