2. Just going off commit author / email (and then corresponding gravatar) seems like enough. I get hand tailoring for something like this, but for a more "general purpose / throw a repo at me and I'll figure it out," I think using whatever you get is ok
3. Could try using tags for this, or I think specifically from Github, milestones / releases are stored differently? Don't know. I feel like this could also be an "include if present or ignore," although I do appreciate how it breaks up the history into a timeline
I don't have any specific projects in mind - for my own playing, I just used my own personal / work repos that I had available on my computer. I think the bigger, popular projects like Angular, React, or even language projects .NET Core or TypeScript could be interesting. I don't know if they would make great graphs or not though, I imagine it would be largely trial and error.