I'd recommend that you look at adding features to calibre rather than writing a completely new application.
calibre provides a cross-platform framework with database and GUI that will provide 90% of the functionality you need. All you'll need to add is the audiobook specific stuff.
And, of course, if developing for calibre, there's plenty of help at the calibre web site and in the calibre dev forums here.
And Python's a nice language.
