Thanks for the quick reply 
About (1) - there's a difference between "Re" and "Red". WD really need to sort out their marketing ! The "Re" are designed for 24x7, 100% duty cycle, the "Red" are just NAS drives. The "Re" are quite a bit more expensive
Having read your answer for (3), though, I think I'll go for the 64-channel NVR with the hot-swap drives. That way I can use 8 of the less-expensive Seagate "Surveillance" 4TB drives while still getting the necessary i/o bandwidth and just replace a drive as and when one dies. This isn't a mission-critical environment, it's my house I just want high-fidelity imagery...
From watching the videos, it certainly seems that the 64-channel NVR can handle multiple motion-detection alarms. Hopefully that's the case at 4k...
Cheers
Simon
