BSD as a virtualization host doesn’t seem to be good, so better stick with Linux.

Sounds good, only thing is a Minecraft server will need more ram. I managed to get Minecraft (papermc iirc) on 4gb, but that ran terrible. I would say 6gb minimum and 8gb recommended if you play with more than one person and want to make a bigger world. Also keep in mind if the server is always running it will always consume this amount of ram if you assign the memory when starting the server iirc. And with that jellyfin also would like some ram, for me it uses a few gigs. But from what I see online it could work with less. Nas doesn’t use that much if you don’t do any crazy stuff.

I used to have 16 and that worked for Minecraft, jellyfin, and various other services at the same time. I now upgraded to 32 and arc eats all of it so non of it goes to waste ;)

Virtualizing an OS can take a lot of RAM, and virtualizing a Minecraft server can take 8GB by itself if you use any mods - I would definitely recommend 16 or 32. The other concern is your storage - for a NAS you ideally want a RAID or ZFS system. You’d need at least 2 drives for this (for whats’ called “mirroring”) to give you some data safety, though with ZFS you can have an arbitrary number of drives and create storage pools with arbitrary levels of redundancy (this may be more than you need though, and would require more RAM as well)

truenas scale maybe? It would love some ecc and more disks tho.