Well...to each his own. I installed car audio professionally for 6 years. As far as mass-produced, I definitely have my preferences, Morel components for midbass drivers, JL Audio for subs, AudioControl for factory integration. The HD series amps from JL are simply amazing. They consistently make more power than advertised and the crossovers are super accurate (in the HDs). In my previous 2008 MKX I removed the factory sub and put in a custom fiberglass box with a JL 8W3V3 (box was .85 cu ft), Morel Elate 6.5 components front and 5.25 rear and integrated with an AudioControl LC7i. That system was amazing, crystal clear, tight mid bass and thunderous sub bass, I miss it.
Do you have any experience with fiberglass? You could really open up your custom solutions with some glass work. As far as running a midbass driver in the rear, I don't think those frequencies would travel far enough from the rear without getting sucked up by seats, carpet and reflections to be very audible.
Good luck on whichever route you decide to take, let me know if I can help with anything.