use-dashes-instead

I wouldn't suggest paying for the upgrade solely for the backup cell Internet

And, to be honest, if you looked into it, you'd probably find it to be cheaper to roll your own entire system rather than dump money into a closed ecosystem

OP clearly isn't looking hard... I have a line with 3GB a month of 5G data (plus unlimited throttled after that) for $15

Best solution: Build/buy a NAS and connect over your network

Second best choice: Stop using a NUC and get a computer with the necessary space for the hardware that you want to use