Using multiple wires on higher circuits

You mentioned using multiple wires and terminals to pass through a bulkhead connector. I was wondering if it could be done with the rest of the system to keep the same wire size throughout for easier concentric twist. Say i have a PMU16 and some radiator fans that run at 50 amps instead of using 2 pins and 2 AWG12 wires can I run it using 2 pins and 4 AWG16 wire as long as the terminals can handle the amps?

yes

That's exactly the technique I used on the v2 of my harness. It's working perfectly.