I've recently bought one of the QuietCool attic fans myself: AFG SMT PRO-3.0, very easy to flash with Tasmota. I tried using Markus' Tasmota drivers initially. They work to control the fan, but cannot report the sensor data without polling. I'm getting ready to try the newer Tasmota drivers by @garyjmilne -- they look great, but I need to hit him up for advice on this somewhat complicated device. (Two fan relays plus two sensors, one for attic environment and another for ESP chip temperature, see below.)
Yours may be even a bit trickier for HE than mine, @emersonvier , since you have a 3-speed fan. But the Tasmota firmware will at least get you realtime access to the environmental sensor, albeit via a web page rather than HE. 
I'll update this post once I figure out how to integrate this attic fan with HE.