NAS unit to supplement 2011 Mac Mini Home Theatre - Build or Buy?

Hi everyone,

I'm gearing up to add a substantial amount of storage space to my home theatre setup. Currently, I have a (late?) 2011 Mac Mini MC815LL/A (upgraded to 8GB ram) running both Plex Media Server and the Plex player. That is HDMI'd out directly to my TV. I don't store media files on the Mac, however; they are currently stored on 5 TBs of WD My Book Live Personal Cloud Storage NAS units. I am rapidly (read: 40+ discs/week, and that number will probably grow substantially) adding both dvd and blu-ray discs to my library and, for personal preference, NOT compressing the MKVs I make from the discs. Therefore, a lot more storage space is needed! I do access plex through iPhone (via wifi) and ipad4 (almost exclusively local wifi), but those aren't used often. One big item on my wish list is a solid setup to allow a couple family members to access the media server remotely through myplex.

I've been going back and forth on buying either a Synology unit + expander (or similar brand), or building a unit along the lines of the UnRaid servers sold by lime-technology.com, etc. I'm looking for a solution that allows for substantial expandability/ future upgrades. I don't have a number of desired disc drives in mind, but I'm under the impression that I likely need at least 8 bays?

My assumption is that using the Mac Mini to act as a head is still probably the best setup. Is that correct?

From a cost v. performance/features standpoint, do you think the DIY option would be cheaper? Same price but better features? Or overall more expensive and not worth it?

Overall, it is important to have a system that requires as little maintenance as is practical.

If the DIY option is better, what are some component areas I need to focus my attention on to achieve the best results?

I'd appreciate any and all thoughts on this project. Looking to make purchases here in the next couple weeks, so please... educate me!!

Thanks everyone!

Charlie