Hello mate, sorry for not replying sooner. Yes, you're right, lower the number, thicker the cable, higher the current rating. 4 gauge is good to at least 100 amps, so you should be fine. Terminate the 4awg at your distribution block, then use 8awg to connect each amp.
Running cable is easy. Remove battery and make a tiny incision in the rubber grommit in the bottom right corner as you look where the battery sits, feed the cable through here, if you look nder/behind the glove box, you should see cable come through, looking up towards the base of the a-pillar. Simply pull up the trim panels and drop the cable in and run down the side of the car. If you gently pull back the seat near the top, you will see a hole giving you access to the boot. alternatively if you remove the seat, there is also access lower down, this was the one I used, and ran my speaker cables through the upper holes.