I voted suspension also. That way I wouldn't have to upgrade other stuff to handle the mods.
With performance stuff like a 3L or turbo, you have to mod the tranny to handle the power, for the audio, you might need to get a 200 amp alternator & beefier electrical supply lines, etc., etc.,
My car right now has a BAT kit on it, & only an intake thus far. I'm likin' it...