Do it all NAS

[TribalHound]

Once you've gone past 'a certain point' - and running multiple VMs is the fastest way to do that - the NAS you end up with will happily add a couple of cameras and not have a major impact, certainly in this performance bracket.

For network traffic, if you're wanting 24/7 recording I'd recommend creating a separate LAN / Virtual LAN. So you have two networks (effectively) - the cameras would go on the second. Avoiding interfering with any other demands.
Since they record to the NAS you can access the footage from either network.

IF, further down the road your NAS starts struggling, or you want to keep the CCTV totally separate, you could get a 2 bay for the CCTV system with an HDMI port you can plug into your TV or a monitor.

Using the Surveillance Station or QVR Pro 'out of the box' means no additional software expense.
You could even utilise an old tablet to live stream the footage that would otherwise have sat in the drawer collecting dust - after all, it would only be streaming data on the same network.

Just watch the camera spec. Avoid Nest & Ring with their cloud option and subscription fees. Make sure what you choose is compatible with your NAS for 24/7 recording (or at least file transfer).
But basically, if it's battery / solar powered it records motion detection ONLY to a micro SSD (which you should be able to copy) - If its mains / PoE it should have 24/7 monitoring and recording, but might not be compatible with your NAS.

Robbie's ventured into some Camera reviews that might be useful, but my personal brand of choice is Reolink.