Needs to be PC and 5 more party slots you can either create yourself or choose NPC's created by Larian.
Period.
I don't think a single character holds the position of "PC", like I said I think the party itself is going to be the "PC" aka the protangonist, I don't think the plot will centre on a single character like it did in BG 1 & 2, Pillars of Eternity 1 & 2, Planescape Torment, Tides of Numenera, Pathfinder: Kingmaker and so on.