So, I've now created a map, with overlays. Now the need to create mouse over events so that people can interact with them.
Here's some places I've found information:
How to make a map with overlays
How to create an event on mouseOver -> with reference to this post
A similar post, but different solution
Not sure if relevent, but a mouseover tooltip for markers
Some docuemtnation on overlay types and Map Type registry