What are you going to do after you wet sand? Polish? Paint? You have to be a little more specific.

If your going to polish then you want to start out with ~1500g then step up to 2000g. If your going to be laying down paint, then you want to follow what the spec sheet of that paint product says. Most basecoats want ~500g. If your going to shoot sealer before the basecoat then you want to sand with ~320g. If your just going to use some spray bomb paint then you would want to wetsand with ~500-600g.

Those are just ballpark figures, every brand of paint suggests a specific grit... If you get back with the brand and type of products you are using then I can prolly help ya out a bit more.
Later/joe