hmm, it depends on the controls... with a wheel it's a huge difference than with keyboard. totally other setups are needed.
i'm figuring out setups myself lately.
i'm working out a season and need setups for all the tracks.
most important things are : wings, anti-rollbars (maybe brake balance but it doesn't effect me much)
the gear ratios depend on your wings and the circuit, really not hard to figure those out (just watch a lap by an ai opponent to know his top speed on the pit straight and figure the ratios out)
the suspension bars don't effect me bigtime either, except the spring stiffnesses... but i'm learning, maybe next year i'll know how to tune the suspension right... for now i'm doing the basics for pro difficulty level