Hi Felix,
Thanks for the reply. I didn't realize that the MHat USB is not for data, so that explains #1. I was trying to program via the Pi in #3. However, I was using /dev/ttyAMA0 but now realize it should be /dev/ttyS0 on the Pi 3. When used that device it worked, so now I have uploaded the MightHat sketch and the LCD is working!
The only thing that is not working now is powering the Pi using the MHat. When I attach the USB adapter to the MHat, it powers up, but the Pi does not. Is there something else that I need to do to get that to work?
Thanks!
Greg