One Step at a Time

As the title says, I'm building up in stages. '07 DoubleCab currently running a JVC single din HU with Image Dynamics components up front and 6.5" ID Co-Ax's in the rear. Looking to upgrade with a 4-channel amp. This one -

http://www.polkaudio.com/caraudio/pa/index.php#pad4000_4

I'm planning on running a 4 ga. power line, as I will be adding an 8" sub and 250-300 watt amp sometime in the future. Expect to run the 4 ga. to a distribution block w/ 8 ga. running to each of the amps. Can I assume that while I'm only running the 4-channel I will need to run 4ga. for the ground as well? Then change to 8 ga. once I have added the amp and sub and running separate grounds for each.

Secondly, does anyone have experience with the amp listed above? It seems to be new in Polk's catalog and their isn't much feedback on the web, yet.