If this is the correct model https://shop.westerndigital.com/en-gb/products/external-drives/g-technology-g-drive-thunderbolt-3-hdd#0G05364 it goes up to 14TB. You may need a bios update but this is unclear.
Non dual control. There is a cable fault or something has become detached or worn. Dual control. There will be a fault with the motor which drives the air direction flaps. Both means that someone will have to pull apart some of the dash to get to these control areas.
There can be numerous things. It may have been partitioned but not formatted? Has it been formatted on a linux system? Has it been tried on another system? Have you been using this before? Go to Conputer Management and click on Disk Management. If it tells you that the disk is Simple, Basic, NTFS it was formatted on a Windows machine. Does it say Primary Partition? If not, then it hasn’t been formatted and formatting will need to be done to make the disc usable.
These batteries tend to flame and smoke when the plates touch. I have never heard of one exploding yet. Always keep yourself safe with Li-Ion batteries. They are evil. I doubt a repair shop will touch it. I would go outside and do it. Disconnect the battery making sure it is not glued to the shell and launch it. If it flames out, no biggy. Now connect your new one.