I'd personally want to support making the player characters during session 0 (maybe not the full character sheet, but at least personality/background and class).

I've done campaigns where everyone came into the session 0 with their characters all ready to go and the idea of the characters being adjusted wasn't really brought up but more the rest of the aspects you mentioned. Differences and some antagonism between characters can make things really interesting, but at least in one of them two of the characters fundamentally wouldn't ever be in a party together. One of the players felt some cognitive dissonance in wanting their character to stay in the party, but not being able to find a rational reason they would, and kinda had to retcon their character.