Vlad, fighter planes or navy fighter planes. Fighter planes with precision bombers or drones, as a shield to absorb the C3s defensive fire, in an attack wing. Forget your off AA batts, you'll need way to many. Dont forget to put a land unit next to any target if the C3 is a neighbour.
10 to 12 countries is about as many as you want on one world really, but you can make more work, seen it done, as long as they really are properly profitable.