I started with a DS216Play back in 2016. It’s been running 7 years non stop. It can serve so much including Plex but the cpu is too weak to do serious transcoding. I recently pulled the trigger on a DS220+. As before I got WD Reds as my older 5400rpm have worked so well over time. You can do your own research but at present only intel based can really transcode.
I use my NASes as the primary storage class in my k3s via nfs provisioned. More recently I setup a functional docker registry and portainer.io instance on them.
I do this for every item. I did buy some stuff this prime day and one item was in reality $5 cheaper… not the $15 Amazon said. I also sometimes find target, Walmart or Microcenter(frys) has just a good a deal: and those stores actually let you return stuff and give you your money back