Hi
1) doorbell don't connect to NVR, you can use 12V adapter and router (or PoE switch)
2) if you use doorbell without indoor unit, you can recieve call and answer/open doors through mobile app
3)yes it does ( DS-KV6113 and KV8113)
4)what do you mean by subs?
5)you can only use DS-KV6113 and...