If the wheel is hot to the touch you most likely have a seized brake caliper. You can often remove the caliper, run the piston in with a c-clamp, and reassemble. It'll likely seize again someday until replaced.
Speakers are cheap enough, I'd buy a pair for the front doors and have them ready at the time of the radio install. You'll appreciate the upgrade in sound quality.
Check out these super mounts, they're the engine side of the motor mount. They use 3 previously used holes and 5 holes not previously used. 1991-2001 Cherokee XJ 4.0L
A good shop can scan the system through the OBD port under the hood on the passenger fender.
This one was translated wrong from when it was told to you lol.
"he pinned the 5v input sensor to the output, and that seems to have helped? Don't know what this means."
It's most often an issue with the full-time transfer case, not the rear end. The full-time transfer case is very finicky about which fluid is used, and dealer fluid is best. Once the viscous coupling in the transfer case goes out you'll have issues, especially when turning.
If they kill your eyes they're improperly adjusted, as are most LED installs in Jeeps. A whiter light is not unsafe for other motorists if properly adjusted.