After all of the above, I found that my setup wouldn’t successfully flash the built code to the Photon. That was because you also have to build/flash the firmware to version 2. See here for details. Now it works.
Also, note that on the new develop branch, the module.mk file has been updated, so my original step 7 above modifications are not needed.
Thanks, everyone for your help. Hopefully, these notes will help others.