As far as I'm aware, teams and cars will be picked after qualifying (no point picking teams now as we don't know what tiers people are going to be in).
I think it was decided that whoever was fastest would choose their car first, second place would choose their car next, third would then choose there's... And so on. Not too sure about this system tbh, as whoever is fastest is only going to build the gap over the other drivers if they get their preferred car, but I can't really see any other way to go about it.