Ok, final question lol. When grafting the piece that I fabricate into the piece I bought, do I need to sand through the gel coat to attach it with the glass underneath? I assume yes, just want to be sure.
Thanks for all your help

Nope, not really, gel coats are some pretty unique stuff.... Since they are the first molded in material they usually have a death grip on the underlying layups. Just make sure the gel coat is clean and hit it with something like 80 grit to establish good profile. There really is no advantage to removing it, just extra work.