Had to read this about six times for my pea brain to understand what happened

Your coolant system overheated because the cap didn't release pressure and the top hose blew, then you decided to get at it from the back instead of from the side, because you have a interstate and figured that was the way, while cutting up the heat shield for access, then you buggered the radiator neck by removing the cap with channel locks because you didn't know about the cap set screw.
Your questions are how to repair the rad and if you need the shield?
Can't help with the rad question, I'd suspect you should look to E-bay for a replacement or try a radiator repair shop.
Much debate over the years on the reason for the shield, but I believe it to direct air passing over the rad away from the rider and isolate the engine heat from the rad while sitting in traffic.
Some riders reported removing it and some of those have reported putting it back.
I will suggest you get your hands on a service manual to prevent further mistakes, but I get it, sometimes you just got to dive in.