You can read/write data without the 30 second wait on the plugindata files fairly easily by using a second plugin that is loaded from the main plugin - the second one will have full real-time access to plugindata files as it loads and can communicate with the main plugin using custom formatted chat commands (not executing the commands, but rather creating and checking for the existance of certain custom formatted commands). If you are interested, look into how TerrainMap loads annotations on the fly as the user scrolls the map.
The mechanism is a little bulky, but its far more efficient than waiting 30 seconds for every external communication and once you've implemented it once, it's easy to re-implement or expand it's usefulness. I wrote a simple chat translation plugin that communicated via an external app with Google translate and response times were pretty decent (of course, some of the translations left a lot to be desired but heh, Google is better than nothing... usually
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Lotro Alerts (sometimes just called Alerter) has a lot of examples of chat parsing. MoorMap and TerrainMap share annotations with each other and with other users via chat parsing. There are several other plugins that do quite a bit of sharing of info via chat parsing.
Unfortunately, I don't use songbook or even work with the music aspects of the Lua interface so I wouldn't be of much help with your other issues but welcome to the neighborhood
Garan