NAS advice needed

Wow, there's a forum for everything!

Here's what I need/want. Basically three things.

1) I own a business that deals with videos (DVDs, Blu-rays). We have about 6TB of video data. We are continually adding to this collection. So I want to have an up-to-date backup of these videos. This is NOT for streaming purposes. Just static data.

2) The business computer itself needs backing up. Probably no more than 500GB worth of data at any one time is on it.

3) Here's the kicker. I would like to use this also as a Plex server for home entertainment. And if possible, I'd prefer that it could eventually handle 4K for future expandability (can/will Plex handle 4k?).

So we're looking at somewhere around 10-15TB or so should be sufficient. But I'm also concerned about processing power for the Plex encoding.

I am willing to buy ready made, or build my own. Any help would be appreciated. Is it possible?

How do you go from 6TB currently to 15TB?

Perhaps have the data from scenario 1 in one pool of 4 x 4TB & scenario 3 in a second pool of 2 x 4TB with scenario 2 stuffed into either.

Having 2 pools will make growth easier.

For the OS NAS4Free would work.

For the hardware how many users do you need to support? A low power cpu with lots of memory will work well for a small user group.

What is your backup plan? You need to guard against hardware fail, fire, flood, etc so an off-site copy is ideal.

Buy a Synology or QNAP.
No DIY that becomes a career..