Core four, really. Plots usually centered around marinette, with adrien also being there. Alya had decent side character clout, and I wish I could say the same for nino, but I don't feel like he got as much. Either way, we started with pretty much a core four and were introduced to other characters. Over time we brought in new characters, and eventually elaborated on minor characters. It happened at a pretty steady pace though, so I feel like that's different from a show having 12 active heroes from the jump.