Outside of what's on the wiki page, you can search our forums for specific information (google returns better results for short length criteria.)
Most of the wiki information is for content..so, code changes will take some tinker->test experimentation.
The code base is highly interdependent within itself and figuring out what is really going on just takes time and familiarization.
If you have c/c++ experience, then you're already ahead of the game
Database access is fairly easy.
If you have access to a database interface gui (like HeidiSQL) you can experiment with queries and see changes in real-time.
I would suggest starting with 'SELECT' queries since they only return information and do not modify any db values.
(If you have grepwin, you should be able to search for 'SELECT' and find numerous query examples.)
Above all else, just remember that the systems works around client requirements.
Changing something to your liking may cause client issues/crashes because it is out-of-scope for the client.