You can then molex to 4 pin fan cables on Amazon. That's for running the fan itself not RGB.
For the RGB part it all depends on the fans. Either they'll include a controller, connect to the motherboard or you'll need to buy a controller separately. If they connect to the motherboard they'll mention stuff like Aura Sync, MSI Mystic and so forth compatible. So, look for fans compatible with the RGB on the motherboard you are buying.