I have two RPi3s running as ADS-B aircraft trackers, one in the loft and one outside at the top of a 10m mast.
One Pi3 is my Unifi controller.
I have a Pi2 running my Pi-hole and OpenDNS server.
I've got another Pi3 running as a NextCloud.
I have a Pi Zero as an amateur radio RX only iGate.
Then there's a Zero W running a secondary Pi-hole.
In addition to those, I have a Zero W with a relay acting as an internet watchdog. If the internet drops out for a set time, it reboots the router.
I've got an internet radio driven by a Zero W.
Downstairs there's a Google Voice AIY thing with a Zero W in it.
And I've got a Zero W as a little play box, so I can test things out and just experiment.
That's four 3s, a 2, a Zero and five Zero Ws. Eleven in total.
I could probably consolidate a little but not much. The Unifi controller really needs a 3, I had it on the 2 along with a Pi-hole and OpenDNS but the performance wasn't great.
The Pi3 that's arriving today is going to be used for some experimentation with a wide band WSPR receiver.