@hybotics I have an original Pi B with 512MiB of Ram running PiHole for my whole home network. Don’t remember the amount of devices off the top of my head, but I can’t see any noticeable slowdowns.
Funny thing is; is barely using 100MiB of RAM. The CPU spikes to some 90% when I remote into it and check the status, but after that it’s farting around at perhaps 30% at most.
I suspect the Pi 0 (or Pi 0W) will perform its task admirably. As long as you can set the Pi as the primary DNS lookup, you should be golden. ?