The Moto X has a habit of requiring a higher amperage charger to restart once the battery has been seriously discharged. The stock charger is only 1.2 amps and can't give the phone the jolt it needs to "wake up" after a deep discharge. Try something a little beefier (like a tablet charger or anything with 2+ amps) and see if that does the trick. There is a hidden green LED underneath the earpiece grill that will light up once power is flowing to the battery. (It only lights up in deep discharge or diagnostic scenarios.) If that doesn't work, it probably means that the little spark you saw when removing the battery was not so little and killed some components.

The TalkBack assistant toggle is located in Settings>Accessibility>TalkBack. The app itself can also be disabled by going into Settings>Apps>TalkBack, and then tapping on the button that says disable. These steps are current as of Android Marshmallow (6), so there may be some differences if you're using KitKat (4.4) or Lollipop (5).

Your best option at this point would be to find an LTE Xoom that someone is selling for parts and harvest the LTE card from it. The replacement is pretty straightforward and can be found in step 8 of the iFixit Xoom teardown HERE.