IMO, 5 characters would actually be ideal and is a pretty common number in tabletop too.
But we need a lot more potential companions and shouldn't be getting forced into using the same ones through 2/3 of the game. What's more, we need some more likeable ones and I really hope they drop the origin character idea and just make them true companions, then focus on expanding how custom main pc is relevant to the story beyond how the others are.