The pinout is here,
Grow HAT Mini at Raspberry Pi GPIO Pinout
There looks to be 10 or so free GPIO, that likely could be used to add more sensors. I’m assuming there isn’t anything between them and the Pi like an ADC etc. You’ll have to check the schematic to verify its just pass through. You’d have to get creative with the wiring to hook them up. A Proto Zero on a stacking header may help with that.
ProtoZero – Pimoroni
The quick and dirty way would be to just cut the connector off of one end of the cable and solder the wires to the Proto Zero.
The python code I’m thinking will be the tricky part, depending on your skill level.
grow-python/examples at master · pimoroni/grow-python · GitHub
Dual or even triple displays is doable. I’ve done both, 2 of those 0.96 LCD’s on SPI0, and a 3 display setup on SPI 1.
You may not even need a Grow Hat. My two multi display setups are the equivalent of an Enviro+, an expanded Enviro+. I’m running a modified version of the Enviro+ python file. BME280, LTR-559, VEML6075 UVA/B Sensor and an RV3028 RTC.
All you’d need is the breakouts and the Grow sensors. Double check the schematic first though. I’ll have a look see myself once I wake up, its just a little after 5AM here at the moment. ;) I need more Java lol.