That sounds pretty resource intensive given the cameras have motion and intrusion detection, and can easily be interfaced for alerts over protocols like ONVIF. But of course whatever you think works best for you.
I suspect the connection limitation is not caused by the Hikvision cameras in this case. The non local subnet detection and corresponding forced connection drop out by the cameras themselves I think is a red herring. As many have said, streaming from the cameras for hours or days to a public IP is common place.
FYI I myself use Linux as a router between public WAN and private LAN using iptables, NAT etc.
You might want to check the below command on your linux router
Code:
sysctl -a 2>/dev/null | grep -e "net.* 300$"