Hard to 100% know until we know how the classes will be implemented, and how companions are ultimately statted, and who actually makes it into the endgame, but I think my gameplan is:
Main Character - Paladin 6 or 7 / Sorcerer X (White Draconic):
Paladin will really depend on Oath implementation. I am leaning Vengeance, but I can see myself going Ancients if Larian makes their anti-spell damage aura OP (in PnP, it only applies to spell damage, but it's very commonly misinterpreted as all "magical" damage. Can see myself going full Paladin too, depending on implementation.
Shadowheart - Cleric X - want someone to see the full Divine spell list with, and Trickery has amazing domain spells in PnP so I would likely want to them fast.
Gail - Wizard X (Divination or Abjuration) - want someone to see the full Arcane spell list with. Abjuration is probably my favorite, but I'll probably be sick of it by the end of EA and want to try something new.
Wyll - Warlock 2 or 3 / Valor Bard X - will go Warlock 3 pending pact implementation
Lae'zel - TBD. Depending on final spell list vs. Maneuvers list, I might go Eldritch Knight or Battlemaster. Might be benched in the 1st playthrough though
Astarion - Rogue/Barbarian. Realistically probably benched
I feel like unless the new companions are very, very interesting, mechanically Gail and Shadowheart are locked for me since they cover the full Divine/Arcane casting classes. Of the remaining 3, Wyll has the most interesting story to me, so he's on the team until we get the other NPCs.
The more I through this list the more I want 6 people party because I want to try the new characters out lol.