OK, so I picked up a used JBL P80.4 amp for $100, and I'm ready to move forward again with this project.
I also think I'm gonna move everything to just behind the back seats in the trunk. I don't want people in the backseat stepping all over my stuff.
I'm revising my wiring diagram and I'll upload that in a bit. Hopefully I can get all of this "done" over the weekend.
EDIT: