Hardware Setup

I am looking into either doing a DIY Nas or a Qnap/Synology (Qnap TS-453Be or DS918+) pre built nas with 12-16TB. I wanted to get suggestions on which is better and why, price isn’t necessary a determining factor, just want to get the best setup. Will a pre built nas even be powerful enough?

If I go DIY what OS (Windows, FreeNas, Linux, unRaid etc) and low power hardware setup should I use to get the best benefits (hardware features, software raid etc etc)?

If I go low powered do I forfeit alot? Does it make sense to get Xeon or will i5/i7 be sufficient? Is it overkill?

Any feedback is welcome!

The end of 2017 I had the same question, but also for me was the (server)case a factor to consider.
i had an old Synology, and was willing to build the perfect Plex server (with lots of expandability) en future proof (for the next 10 years or so)

Read my conclusion at http://forums.plex.tv/discussion/301328/new-nas-tvs-1282-or-ts-1277-and-update-story/p1
and i am so happy with this thing, the i7 with hardware video is a must with multiply connected users.