Bricked Galaxy Tab A. Help? Please
Wiping /data and /cache of course won't help because Xposed writes to /system.

EDIT: As @DeathMaskSalesman points out in the comment, you should try the Xposed uninstaller available in the official Xposed thread. If that succeeds then great, you won't need to continue reading the risky part!

The Xposed zip shouldn't have allowed flashing on a wrong SDK at all, but now that the damage is done, back up data (internal storage) via TWRP first (you've already done a factory reset so I assume no app data needs to be backed up), then flash a factory firmware available at SamMobile with Odin to get a fresh start.