New Raspberry Pi 4 is out!

I’d recommend something with reasonable Ethernet and a fast disk interface, so the Pi 3 isn’t going to cut it. The Rock Pi has better passive cooling options and an M.2 option, which is nice, except that its large heatsink and the M.2 interface collide, which is not.

Alternately you could use a GnuBee which is a board that has six 2.5" or 3.5" SATA connectors and needs less power.

You can build and run the storage node without Docker: