Extremely detailed build! Thanks for putting ideas in my head.
I want to add my experience, but please note I am a bass head (SPL stuff). I currently have a 15" Soundqubed (SQ) HDX3 running on a SQ 2200D at 1ohm, its in a 3.5cft box tuned to 30hz. I haven't metered it, but its loud and respectable in my opinion. Its not making people tap out or anything, but its in your face bass. Surprisingly, stock electrical is holding up good too.
I have always hated on Bose, but I will say - When you turn bass -10 or -12, the mids and tweets are greatly improved on the stock Bose speakers. Historically, I could never add this much sub to an older vehicle and get away with stock speakers. I always ran amplified mids and tweets prior. These scream and are loud enough to play along with the subs. However, in terms of sound quality, I know many would complain.
I wonder for ease of trying, should I attempt to replace the A pillar speakers and/or door speakers but keep them on the same Bose amp? I know they can be weird impedance speakers. I really don't want to wire a new 2 or 4 channel amp, just seems like a lot of work. I haven't been able to find write ups about this but seems like based on your experience, its pretty easy to swap out those speakers.
Thanks again for detailing your build!