1. NVRs can work, but you have to be careful and read all the specs. For example the one you linked says it will accept 32 cameras, yet under network bandwidth it says "Up to 80 Mbps input" which is just 2.5 Mbps per camera. That is well into the low side. Now in all likelihood you won't actually run 32 cameras and you'll actually be able to use 4+ Mbps for each camera which is much better. Just something to be aware of.
2. Lets assume you are using the entire input bit rate of that NVR above. Google can calculate this easily:
(80 Mbps) * (2 weeks) = 12.09600 terabytes. 12TB of actual hard drives is likely to only deliver 10 to 11 TB of usable space, of course. That is a respectable 5 Mbps per camera for 16 cameras.
3. I recommend Hikvision too, as I've had better luck with them than with Dahua. There are others who will say the opposite though.
4. No issues as long as you have adequate internet speed. Yes, multiple mobile devices can access at the same time.
5.
DS-2CD2532-IS. It is pretty small and I think it has a built-in microphone ... though there is a no-audio version of this cam, so be careful. I don't have any of them myself.
DS-2CD2432F-I is an entirely different style, but I have one of them and audio capture works well with its built-in microphone. You can turn microphone volume down to 0, but if you have a location where audio capture is prohibited it is probably best to just buy a cam that doesn't have a microphone as that will give you more options. There are other cams too, just look through Hikvision's product library. Be aware that any dome with IR LEDs behind the same glass as the lens has an increased chance of IR bleed causing a foggy picture in the dark.
6. Both will work, cat6 is more future-proof. Do not buy cables that are made with copper clad aluminum (CCA). Only get solid copper cables.
7. The built-in PoE on an NVR should be fine. Otherwise they wouldn't include it.... External POE switches are often compatible and can help with connecting groups of cameras that are far away from the NVR. External POE switches are of course a necessity if you don't run an NVR with PoE ports.
8. Most IP cameras by Hikvision are rated to -22 F / -30 C so they are fine in most climates without any extra effort. Putting one in a fridge or even a freezer is fine, though I don't know, maybe fogging could become an issue due to all the warm air coming in the door all the time.