I've recently gone through building a NAS for home. I read several guides like this, but a lot of them didn't quite match what I had in mind. Following some takeaways from my personal experience:

- Finding a low-wattage/high-efficiency ATX/SFX PSU is the hardest part. To achieve the advertised efficiency, your Gold-rated PSU needs at least 20% load. I.e. 100W for a 500W PSU. If you are building for low-power, you will need much lower wattage for the PSU to operate at optimal conditions/efficiency. Good luck finding anything under 450W these days.

- Do your math before choosing RAIDX, where X != 1. E.g. the disk cost for 2*16TB RAID1 array is pretty close to the cost of 3*8TB RAID5 array of the same capacity. But future upgrades with RAID1 are much easier and less costly, given that your NAS box will probably have only 4-5 slots. RAIDX make sense if you want to go wild (target NAS capacity >> maximum available single disk capacity).

- If you have not jumped into the "homelab" rabbithole and you only want a NAS and some services, NAS operating systems like TrueNAS are a PITA. Your hardware will be "owned" by the NAS OS, and you will need to jump through hoops to get any other software running. Most of them encourage you to not run anything else on them, except from prepackaged apps from their "store". So, you may want to stick with something more prosaic. E.g. vanilla debian.

- If you are thinking of ZFS/TrueNAS because of the scrubbing functionality, RAID1 + BTRFS also have scrubbing.

- Motherboards from AliExpress save you time. If I could procure a motherboard with 6 SATA ports, at least 2 2.5GbE ports, and an N series CPU from a mainstream vendor, I probably would. But there aren't any such models. If you try to add these features on top of a standard motherboard, you need another round of researching components. Plus, if it is a mini-ITX mobo, you may run out of PCIe slots.

- Motherboards from AliExpress are just fine. I'm not sure why people nag about "reliability" without even anecdotal evidence. If your mobo dies, too bad. But mobos are pretty low in the list of components affecting the safety of your data, with PSU, disks and software being more important.