I’d probably go for a small N100 mini-PC.
Should be plenty powerful for what you need, very low wattage and relatively trivial to get GPU pass through in Proxmox. Alternatively one of the more powerful versions.

This depends on how many cameras, resolution and frequency of course, but you should be able to see if others with similar setups have it running smoothly. You’d be limited on storage, but can set up NFS to your NAS or existing server.

I plan to use Surveillance Station in my Synology NAS.
Two PoE cameras on their own physical network. Everything is laying in the closet still as life just gets in the way, but hopefully it will be done this winter or spring.

I also have a Eufy 2k Doorbell camera with a hub for local storage.

None of it is for actual protection though, as burglaries are rare here. It’s only because I love tech and to capture interesting moments. I also plan on making time lapses because they are cool.

I agree.

It’s easy to forget how much time and dedication running a custom setup can cost, and that quickly drains whatever wife-acceptance-factor you had left.

Think of paying for a pre-built NAS less as just overpriced HW, but more as great software features that work out of the box and a dev team improving functionality for you every day.
It can host a plethora of containers with ease on the side anyways, and if you need something specific that requires more juice: build that on the side and tinker with it.

N100 mini-PC for instance can host anything but heavy game servers for <15W.