Before I upgrade to 2 TB I want to make sure it will finally be easy and fast to add content to it simply. Like maybe while I am sleeping or away from iPad for a little while.
Anyway to set this up to do automatically? Guessing not 
I gave up on 4g lte / 5g being enough for high quality video to stream reliably without buffering.
Where is the media stored outside of the iPad and how fast are you looking for?
My computer.
10 hours or less to fill iPad
Well that works out to 466Mbps to fill 2TB. Over WiFi that is going to be hard. Hardwired might work though. Over usb it could work, but not sure how to get it easily into infuse. I think you have to copy to infuse after it gets into the files app.
A USB transfer is probably your best bet, and this can be done using the Finder integration described here.
Note: Transferring in this way doesn’t provide a great way to view the progress of how much is transferred, so it’s kind of a start it and wait sort of situation. You might consider starting with a few files at once, instead of all your files.