I built a NAS almost a year ago and it has been rock solid. I'm running unRAID which I love. I'm not using a ton of plugins/dockers like some people do, or using any VMs, so it's all pretty simple which matches my usage.
NAS Specs:
Supermicro X10SL7-F motherboard (pretty much stole it - got it for $50 off eBay)
-Main benefit is 14x SATA ports (8x are combo SAS/SATA), so I don't need to mess with drive controllers.
Intel Xeon E3-1231 v3 CPU (I think this was around $75 on eBay)
Noctua NH-U9S CPU cooler
32GB (4x8GB) DDR3 ECC RAM (~$120 on eBay)
Supermicro SC743T-500B case - comes with 8x 3.5" hot-swap bays, and I added the Supermicro CSE-M35TQB mobile rack which converts the 3x 5.25" bays to 5x 3.5" hot-swap bays. (Case was $330 on Wiredzone, and the mobile rack was $130 on Newegg)
32GB flash drive (plugged into the motherboard's USB port) as the boot drive
1TB SSD for the cache drive
14TB HD for the parity drive
58TB of total usable storage over 5 drives
This leaves 2x of the original hot-swap drive bays free if I need to expand. I use the additional 5x hot-swap bays for my backup drives - I keep those in drive cages but disconnected, so I can just slide them in whenever I need to back something up. I'm so glad I got the X10SL7-F, because with the cache drive and 13x hot-swap bays, all SATA ports are used up.
I saw some people going with gaming/non-server equipment on their builds, but I decided to go all-in and use only server equipment, and I'm glad I did. I recently bought some rails for the case, so I'll eventually mount it in a rack. I also recently bought an APC SMT1500RM2U UPS, which will also go into the rack.
The only dockers I'm running are Krusader (for when I need to do any file management between the drives), and FileZilla.
The ipmitools plugin is a must if your motherboard supports IPMI - I've got it controlling the fans, which keeps the server pretty dang quiet and at reasonable temperatures. The Unassigned Devices plugin is also a must. I use this to manage the backup drives, so that they aren't part of the array and are seen as separate drives that I can do whatever I need to with.
I have two primary sharing accounts setup - one which can read/write all shares, and one which can only read certain shares (i.e. does not have access to my Documents share, but can access Movies/Music/T.V. Shows/Games). I have my HTPC, which runs Kodi, on the read-only account. My desktop and laptop are on the read/write accounts, so if I ever need to transfer anything to my server it's nice and simple. All PCs use the standard Windows SMBv3 sharing, and it has been problem-free.
At some point I might setup Wireguard so I can access my NAS using a VPN when I'm not home, but I haven't had a need for it and it's probably better if I just keep it contained to my home network.