Wire gauge and fuses for Alternator upgrade

I have a 66 cuda and would like to keep my original look and functions where I can (battery cables, electrical gauge, etc).

But in adding a stereo with amps and a few modern items I know I need to run a new heavy duty circuit (4 gauge from the battery a fuse/ then into a 3 way terminal and separates out 8 gauge to the amps and another fuse box. (I'll also add a couple relays for this to allow things to turn on with ignition power not just power all the time).

However my concern is my alternator can handle it and I'll need to up it. In doing this I figure I'll need to up the gauge of the tiny wire from the alternator.

If I do that and allow a path of least resistance, even a higher output alternator should be good no? Even if I leave the gauge connected? Anything I'm missing or places in the original wiring that I also need to beef up or where to add a fuse/breaker/fuseable link?

Thanks