If you're expecting bass from those 12 inchers, yes. You will need an amp.
See if you can go online and find an installation manual for the amp you're looking at. It'll tell you what size power cables you'll need to feed the amp. If it's a 600 amp max output total, you'll need either 8 gauge or 10 guage wire. If it's 600 amps per channel RMS, you're into 4 guage or larger territory. Regardless, get good connectors and make sure your amp's wiring has a separate fuse.