Best build for 6-10 disks

Hi all,

I'm looking in the forum for some tips about a fresh build for a (free)nas.
I have 6 disks, but I will update it later up to 10 (size may vary from 1 to 2 TB).
I will use that nas as a fileserver and I will use to send films to tablets (in same network) with Plex.
I would like to spend about 200-300$ (200-250€ because I live in EU).
Mainly I was thinking about this config:
CPU: AMDAthlon X4 860K
MB: ASUS A88XM-Plus
Case (already own): Fractal Node 804 server cube...

Best build for 6-10 disks