I'm somewhat in the same boat, same aspirations as far as recording that number of cameras, having some flexible viewing & reviewing abilities.
Though with more of a value budget, carefully weighing options.
I've been going over the synology NAS specs several times of how many fps at what resolution they can handle, but it just doesn't look future proof enough. You pay a premium and are right at the edge of what the disk station can handle. Synology recommended I get their core i3 rack server for a few grand, empty! Then you look at what pc hardware & cpu power you can buy for the money. I think the NAS are just a step or two behind when it comes to power (too focussed on low power, thermal, compactness, ...) and while great multi-purpose devices, and I like synod's surveillance station; it costs a lot to dedicate a fast disk station to surveillance duty. The redundancy of all the recordings isn't important really. Doesn't have to be x drives in RAID whatever. Looking at the feed from an individual 1920x1080 camera in h264, it pegs around 1MB/s. It might max out at 2MB/s at higher settings (and maybe 3mb/s at full 3meg?) I still have to play around more. The critical things is just that it gets recorded. And many times simpler is better.
I agree that a 4k display would be a nice screen to monitor all the feeds simultaneously at a large resolution. I have it in mind as well. But, I would wait on a 4k display till the market matures a bit more. There's some issues driving them with current hardware, screens with only 30hz refresh rates, having to use two ports to drive one, compatibilities, ...
And, reality is that, imo (which is amateur and surveillance novice but some security knowledge), you don't need to see every detail in the mosaic. Just the overview is fine. I've got 4 3MP cams set to 1920x1080 up on a regular HD pc screen, in 2x2 or 4-up mosaic, and you can perfectly tell what is going on. The scaled down view of the HD is better than a lower quality sub-feed. Also is better than what we used to see as analog in mosaic on ordinary tv monitors. I have no doubt full hd would be fine for live viewing with 3x3 up. Of course one cannot read every single detail at a distance, but you get the view. Double click and it pops up full screen, if you 're behind your desk.
But again, the most important things is that when something happens, things get recorded in high detail. Then you can review in detail later what was recorded.
PS: I'm giving a fast intel nuc serious consideration. An older core2quad test pc I have is starting to complain with the 4 cams connected and I'd rather not have a tower pc sucking energy 24/7. I have enough vampire load as it is. And an OEM NVR where cams are plugged in directly isn't flexible enough installation wise where the nvr would be vs long retrofit runs to get the cables to the cams.
