Usually the BIG 3 upgrade only consists of the following:
Battery + to the Alt +
Battery - to the engine block
Engine block to chassis
Why do your audio system ground to your battery? No need, its rather a waste of wire. Typically, run the 0 gauge from the battery to the distro block then from there run your lateral amp wires (fused side of course) to the amps with 4 gauge, which usually can be within a few feet of the amp. Choose a point close to your distro block location for your system ground. Grind down the sheet metal to bare metal for good contact point. Then run 0 gauge from this point (bolt it down using a ring terminal), to your distro block. Run the same size wire, 4 gauge from your amps to the distro ground connection.
No need to uprade the starter wire, this doesnt draw as much amp load from your battery as the audio system, again, just another waste of wire and $$. Here is an example of my distro block. All 4 gauge wire, power feed and ground are on right hand side, lateral lines to amps are on the left. The main ground position is about 2 feet away from the distro block. The battery power, well comes from the battery.