This is a post that will experience ongoing updates, as it is meant to help chronicle (and assist me in remembering) how to do this. Hopefully I do publish on Sitepoint's WordPress channel, and it all works out in the end. As of 10 May 2016 I've got bunches of ideas, and am taking the first baby steps.
Github and Trello
One good sign is that Sitepoint's WordPress channel, among other channels, use Trello for idea submission/discussion/approval and Github for peer review. These are great tools and processes.