You'd get more attention if you started your own thread for the questions instead of burying them at the end of this thread.
For a car equipped with enhanced Autopilot, I'm not sure how you can tell if it has paid for Full Self Driving. There are options in the center screen that only show up if the car has the features, but right now there aren't any that are in FSD but not eAP to see (that may change soon, or may not.)
My 2016 had no FWD issues, my 2019 hasn't so far either. YMMV, but I think the majority are fine.
Maybe you mean versions of Autopilot hardware (AP)?
Everything except AP1 is supposed to be upgradable to full self driving. I'd suggest at least AP2.5, because they redid the car's electronic architecture and created safety redundancy. Right now we aren't aware of any differences between AP2.5 and AP3 except for the AP computer, which will be upgraded for FSD.
No 6 seat X has ever folded the middle row, including current production. Every 5 seat is folding. The 7 seat changed somewhere in 2017 I believe.
I don't know how to answer your cost question. The only routine costs are electricity, washer fluid, tires, and depreciation. The cost of electricity varies widely by location and charging method, and the rest are generally insignificant, except for depreciation.