I worked on my first migration oft a Plone addon to Python 3 during the last days. There were some instructions available on Github how to procide and I followed them. I was able to run the addon inside my local environment, but I got some issues with the continous integration test on Travis-CI, once I submitted a pull request. I had to fix the scripts inside the addon for building and testing on Travis-CI and was successful with the great support from a member of the Plone community. He merged my pull request and released a new version of the addon cioppino.twothumbs today: https://pypi.org/project/cioppino.twothumbs