With FreeNAS you have a debian based OS with all features for a NAS and is more powerful and manageable than Umbrel.

Nice! That one looks decent, I'll check it in more detail. 

Yes, I'll definitely put something linux based on it either way. Is there a specific reason for why you are recommending FreeNAS (vs for example just running Debian on it, or flashing Umbrel)? 

nout

Then go for Pantera Pico, the smallest PC ever.
https://picopc.net/
And install FreeNAS OS on it with all your need.
But is not the same powerful as a NAS. NAS is not designed to travel with. Is more to be left at home and access it wherever you travel.

DarthCoin

tech

What is the best mini/micro PC for home, media and fun?

Yes, that one is almost good, but 1.5kg is bigger than what I'd like to put in a 23kg total luggage that needs to contain all my stuff. 
I agree that NASes are generally the same thing as what I'm asking for, but my main issue is the form factor. Do you know about any specifically small factor NAS? 