I would suggest a SD Card for Backup. If someone breaks in your house and steals your NVR and or your Ext. Backup would would still be able to retrieve video (motion triggered) from your SD Card...
We have a general rule here that No Camera should have Internet access (Be able to Phone Home) as we refer to it. If you plan to use the ReoLink App (Their Cloud) it would be best to have the Camera Isolated from the rest of your network. VLANs are one way to do this but require Managed Layer 2 Switches, another way would be to have
a second network adapter/card on your M1 Mac Mini which would put your Camera on a different subnet than your private network and a third way would be creating Firewall Rules but this usually requires a router like pfSense or OPNsense. I would look into the 2 NIC solution...I can't help you with MAC but you should be able to do a similar setup like this one:
In making your system more secure this is a great option to eliminate your cameras calling home / connecting to the internet This is a great place to start to setup a bit more secure network and learn more about IP/Subnets etc. before adding dual NICs: Router Security - Subnets and IP addresses...
ipcamtalk.com
So to answer your question about 2-way talk, the Reolink App will allow this, don't know anything about the NVR software you are going to use, you may want to check if it supports 2-way talking.
Blue Iris here presently does not.
I think the Rich Notifications on the POE was an issue fixed with firmware, but not fully sure.
I don't use their App so not sure how many Users but in their local client software it looks like you can add quite a few family/friends
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HTH