Strange, I wonder if that was the SD card or one of the SATA drives? I mirror my data between the two HDDs for redundancy and occasionally run remote backups, though I've never had any problems with data loss. Been running mine for 2-3 years.
If PCI-E is a must your best bet (with least headaches) is still something x86 based, and for the lowest power you'd want something like a celeron-N or J series. For example this board: https://www.asrock.com/mb/Intel/J5040-ITX/ has sata, m2, pci-e, non-soldered RAM and will idle at ~6-7W (excluding storage). If I were doing it, though, I'd spend a few extra watts on an i3-10300 or later, which will idle at maybe 10-12W (again excluding storage) but give you much better performance and much better hardware assistance for video transcoding if you're going to be running plex/jellyfin or an OTA DVR. I use an Asus PN-41 miniPC with an i3 10300 with a couple of USB-C HDDs as an offsite backup server, and it idles right in that range plus about 5W per attached disk (when not spun down).
Hardest part was mounting everything in my 1U chassis. Using an ATX power supply with the break out board solved a lot of problems. That way the SBC gets 12v, and the sata drives get power at the same time. And you've got connectors for fans and stuff. You can use a smaller form factor PSU. I think mine is like 200W but that's more than enough to power the board, expansion card, fans, and drives.
On the software side, I just use the Debian based distro "Armbian". But it looks like you can use others.