Yep, saw those vids and they're great. Just double-checking to be sure I'm clear on my path forward. You didn't use the RCAs on the Metra harness, correct? You ran new RCAs from new headunit to new amp?I covered all of #2 in pt 3 & 4 videos. To recap, I brought the power wire for my amp in through the firewall on the passenger side. You'll run RCAs and a remote turn-on to the amp. Also, if you plan on doing a subwoofer, you can run your sub gain dial wire as well.
The metra harness will connect to the radio harness coming from your truck. You'll connect the wires coming from your aftermarket radio's harness to the metra harness. Then yes, you'll do the antenna separately. I have XM and have yet to connect my FM antenna.