Wordpress is extremely powerful and although there are no online courses to get you started with customizing it, there are dozens of great blogs for all sorts of customization, from basic theme edits to things such as inserting posts to the database programatically.
I recommend checking out a few of the following:
http://wpengineer.com/
http://www.catswhocode.com/
http://wpshout.com/
http://wphacks.com
http://www.smashingmagazine.com/category/coding/
Smashingmagazine doesn't feature solely wordpress in the coding category but there are some greats tips if you filter out the irrelevant posts.
And have a decent idea of what you plan on altering about wordpress - since you don't specify what you deem as 'elaborate'. My advice would be to start off with a powerful layout with a lot of backend customization and work from there - or if you are really willing to take the plunge try coding your own, its actually pretty simple.
Most importantly though - If you have any knowledge of PHP you should use the Wordpress Codex since it has every feature of wordpress documented with very clear instructions on how to use with the different parameter and quite often examples aswell.
Good luck!
