I am running bags with a dual compressor setup, and will be adding a stereo later. Big Dave gave some excellent advice, but I would say alternator upgrades are normally a good idea on any older vehicle when you want to put some modern electronics. At idle, these older 60amp or lower alternators don't even put out enough to run windshield wipers and headlights, let alone anything additional without adding draw to the battery.
I ran 0AWG OFC wire to the trunk to a distribution point that I can then tap off of for anything additional I need. I also have a ground disrtribution point that is direct run down to the frame. I run a small wire that is hot when the key is on to a switch, then to an SPST relay to engage the compressors. I added a hidden switch because right now the compressors are a bit loud, and sometimes I don't want to wait for them to fill the tank if I'm already at drive height, so I can just switch it off (without waiting for the auto pressure shutoff). I have done the big three wiring upgrade as well, and have a new alternator ready to go in once I swap the motor.
You can always go larger with your ground, but don't go smaller with regards to wire size. Big Dave was a bit conservative on amp carrying capacity, which can actually change with temperature, but a good OFC wire like those sold by knuconceptz or other quality brands, can actually carry around 80-90amps at 25ft. 60amps is still an excellent safe number, especially given the number of cheap brands that claim 4awg but it is mostly insulation and not conductor.
If you go with copper clad aluminum (CCA) it has more resistance, so can't carry as much current over similar lengths.