Creating an in-player plugin for the HTML5 Player

I’m attempting to write an in-player plugin for the HTML5 player and am not sure of the best way to accomplish everything I need to do.
So far, I’ve managed to modify the player uiConf and have added some HTML elements to the player using the example in the documentation, so I think I’m ok on that front. As part of this project, I also need to be able to pull timing data so I can trigger the player to do certain things at specific times. Right now my thought is to store the timing data as an attachment asset (xml file). I will also be storing thumbnails as attachment assets.

Does anyone have any suggestions on the best way to do this? Is there a better way to store the data than as an xml file? Can anyone point me to a code example where data is being loaded by the player plugin for things like thumbnails?