I agree with Massamuusi that if not attacking then you will be attacked and attacking and withdrawing can give you some respite (they may also be more inclined to ceasefire?). Also if those provinces rebel then its not really conquering if you take them after that...really.
I have been at war with this many factions before but not usually in early era and biggest problem i had then was NO TRADE. So if intent on GA and not conquering then ceasefire missions maybe needed, although they don't seem to work very often.