Moving from a Mac Mini

[Andyroo]

I'm currently running the server on an old (Late 2012 i5 dual core) Mac Mini running Debian and with all of us watching the poor box struggles some days to cope (esp if I fire up an iPad client) but am limited for space so have been looking at the NUC type boxes rather than the SFF Dell or HP style machines.

I've been through the requirement specs and found a nice box in stock with an i3-1220P but wondering:

• Windows or Linux (Debian / Ubuntu preferred) and why? I'm happier in Linux than Windows
  
• Memory - thought 16GB or 32GB max - the Mac has 16GB and runs five or six containers and is not constrained but a thought is to use some as a disk cache if transcoding needs / can use it
  
• Run the OS off the nvme slot and use the 2.5" for media. Not sure what HDD are like for 4+ users and a 2.5Gb Ethernet network to the core switch then 1Gb to each user.
  
• I may need to use an external drive as media overflow though as the box will only take 1 x 2.5" (7mm Z depth max) and I do not want it on the OS drive (old habit). 
  
• Media / system backup to USB drive directly connected (and off-site rotation)
  

I'm estimating 4 local users (PC / Mac clients) with 1 iPad client and around 200+ films in mkv format (once I've spent 6 months ripping them). The switch is not constrained for packet throughput and all clients bar the iPad are Ethernet connections.

Am I missing anything to research / think about?
What do you think of the spec?

I am squeezed for space and the Mac Mini format is as large as I can go (the backup disks will sit on the floor - the overflow possibly a 2.5" external SSD sat on top)...