I built a box with a standard PC case and a xeon v2 wfor zoneminder, and just slapped a second hand hyper 212 evo on there

I would say go for a v4 over the v2 because the efficiency is much better. You will probably just want 1 core per camera + a few to account for OS + container overhead, so more cores + efficiency is better here

I have some crappy reolink cameras through a unmanaged POE switch, up to a managed switch (cheapo tp link gigabit) so the camera and NVR are on one VLAN. I set some firewall rules in my eouter (edgerouter x) to let me connect to the NVR but block the cameras. Not ideal, but it works.

Perhaps better would be to use a NIC and connect directly to the unmanaged switch so there's no need to VLAN, but I'm not using this for anything crazy, and i can still get gigabit speeds to the NVR

Also using a used enterprise 6tb drive for storage. Works fine and has been going strong for a year. They're a fraction of the cost of a new drive, and are usually pulled well before theyre ready to fail