I have an old HP Microserver G8 which I upgraded to a xeon processor and 16 GB of RAM. Currently I'm running Unraid with 4x 8 TB HDDs plus 2 external 4 TB drives.
I't's been happily running for 5+ years. I don't intend to change it anytime soon, but if I was building a NAS right now I would just use a big old PC case with plenty of space for drives (2000's-2010's era cases are great for that) and use a low power Motherboard/CPU with unraind installed.

If future expandability is not one of your concerns and you don't want to mess around with hardware/software maybe stick with an pre-built NAS from Synology or QNap. You pay for the convenience I guess.

Should you have a JBOD availble, maybe use It connected to a low power Intel N100 mini-PC and call It a day. the integrated GPUs on those things rock for video transcoding if you need it!