I have two mini PCs, one has an old Atom processor, and the other is i5-4570T. Not sure of the power consumption. Both run Linux with no GUI. When I run torrents on the Atom when downloading at a high speed I can't access the torrent web interface, the system can't handle the workload, so I just wait. My i5 has been handling everything4 fine. I run HandBrake on it for movies. It's slow, so I start it up before going to bed. Again I don't know what the N100 can do.
If you want to run Plex you'll need to see how N110 performs at transcoding. Personally I have my media server NFS mount my media. Then just play it as a local drive.
You can get a cheaper unit than the Beelink with a i5-6500T.
https://www.youtube.com/watch?v=Ureon327LrE&t=984s
With the Dell you can have a 2.5 HDD which would be cheaper. Again it may use a little bit more power, but the system would do more.
Hope this helps.