Building a Plex server for an Xmas pressent.

Hi, I am planning on building/buying a Plex server for a friend as a Xmas present. I just wanted to make sure I have done my maths.
Their only experience with plex has been using it on their tablet via the android app and their laptop (my home server via remote ).

They are tech-savvy enough to know how to update the library via a laptop once we go through a quick 10 min refresher lesson. I was thinking to get a cheap Dell 745/755 (Q6600-8MCache Quad core) 8gb ram. As far as i can figure out from reading all the plex website Q&A i think this will run a laptop and ps3 and a tablet device of some sort (on a 600N network with server being plugged in by gigabit)

As far as server ok I was going to set it up as windows 7 pro x64 as I have a spare license for that, Due to them being disabled they still qualify for the windows 10 update until the end of DEC 2017 I think. on that note does anyone have any thoughts on 7 / 10 … the pc will not be used as a pc, it will just be a server / NAS setup really. ( though once they get used to it they may use it with the living room tv so i stuck with a std windows operating system.)

Believe it or not, I would go with the update to Windows 10. Once you have done the update(and activated) then downgrade to Windows 7. I say this because you only have a limited “eligible period” and once the eligible period has lapsed, you lose the free upgrade.
This way you can get the digital entitlement created for that hardware and at anytime in the future you can upgrade back, or even still, clean install to Windows 10.
BTW, I hate Windows 10 but why lose a perfectly good free upgrade.

I admire ones thinking sir, Most Admirable! Mr. Rimmer would be so proud!