[SDPhantom]

I would suggest starting by working on small addons to do some simple things and building up your understanding of the system from there. Nothing will burn you out faster than to dive into a fully customized UI and scramble to attempt to understand what's going on. I suggest starting with the game and widget APIs. After you have a good handle on the core concepts of the environment, then you could take a look at the Ace framework and other user-created libraries. Many addons use these libraries, so knowledge in them would be helpful when debugging.