FYI I have some info going in another related thread:
I had to use (0x5E) as the seesaw address.
Regarding the Adafruit_GFX library, see the comment below from the other thread:
I've begun to work with Particle Workbench and am getting to like it. Adding libraries as you mentioned is a piece of cake, but you do have to get to know a new platform. It's happy with the new generation of devices, and I'm sure as i get to know it better I'll like it even more.
If you get this display running, please share how you did it!