While I agree with others pointing out the oddity of a portable server in general: this sounds like a great use-case for a laptop.
Built-in battery, wifi you can broadcast out as a hotspot, and it even has a display/keyboard/mouse for troubleshooting!
An older laptop with the optical drive stripped out could have a 2.5” 5TB HDD in addition to the boot drive for some decent mobile storage.
How do you get better at playing the guitar without actually playing the guitar?
(edit): Point taken, but “playing the guitar” still wins by a mile