Our Open Graph plugins are where you'd want to put all the logic. You shouldn't need to modify Zoo at all, if we've done our job right with the structure of our code.
We're in the process of working on full documentation for the Open Graph plugins. However, if you know Zoo decently well, then copying and editing something like our EasyBlog, K2, or Content Open Graph plugins should hopefully get you going. The code for each of those is under 200 lines each, and you really shouldn't have to do much more than change a few lines to update for the com_zoo query param and differences in the query strings.
We don't have any examples now for 'post when new content is created', but it would follow the same flow as 'voting' in both K2 and EasyBlog... look for the specific action being taken by the user (voting, new article, etc), doing some checks to make sure everything seems right, and then calling the triggerAction function.
Hopefully, that gives you some ideas on where to start if you're interested. Documentation should be available over the next week or so, and we're hoping to get a Zoo plugin out over the next month or so (with lots of caveats in case we get distracted or it's more difficult than anticipated).
Best of luck,
Alex