I’ve been using FreeNAS for about a year. The community has the angry sysadmin mentality and they favor retired sever hardware but it’s not hostile or anything. The docs are decent and setup isn’t too hard. Make sure your rig can boot FreeBSD.

OpenMediaVault is another Debian based distro I might check out in the future.

Hardware wise I’d go with something that supports ECC and a sever grade mobo, likely intel based. Supermicro has some cool IPMI features I used to setup over LAN, no monitor or keyboard.

Just a reminder to not open up your NAS to the public. I VPN to my home network if I need remote access.

+1 for FreeNAS. I recently converted my Mac mini 2012 into a FreeNAS box, I just replaced the SSD with two 2.5" HDD. No ECC but also way cheaper than the alternative I had in mind.

Ssh/sftp can be open.