12 Volt Solar panel for 4 6v batteries in series parallel

Thanks. So which battery terminal would I hook up the alligator clips? I think I'm going to go with 200 watts solar and a 30a controller. it says it can handle up to 400 if we need more power. In the long run if I do a nice system like yours (1000W solar) all i would have to replace is the controller and buy more panels correct?