As a note, the only fan switches available are Z-Wave which would require another hub. The switch posted above is only on/off so you would be not get speed control, plus you would need to reuse the wiring in the switch box. You mentioned you were using the wiring for something else. As a note though, that switch is one of the only compatible with a fan and the Echo Plus.
There is a ZigBee fan module available at Home Depot but I don’t think the Echo Plus supports it. They may in the future but as of now you’d likely need a SmartThings or Wink hub. That device has 4 speeds and needs to be installed in the fan canopy.
Also, there is a device called Bond. Several community members like it but I don’t know it’s specifics. It will work with the Echo Plus (or any Echo as it is WiFi). I believe your fans need to have existing remotes. It can also control multiple fans and should support 5 speeds.