I hesitate to discuss it less I manifest people looking for a fourth poke way too early, but I feel like the main thing I want in terms of team composition is a fighting type, since we've got a quartet of Dark legendaries on our long-term agenda, and also we should get into Andosin martial arts when we can, plus we've got multiple instances of Rock, Ice, and Normal on the gym list, with Grusha in particular looming as a fuck-you to Roland and Ruby.
For the remaining 2 I feel like you can never go wrong with any of the game's trillion Water-types, Tinkaline is still an option as a solid pokemon all around, and if Paldean Wooper comes up as an option I'm obligated to bribe, threaten, and blackmail whoever is necessary to get it to win that vote.