For extending/modifying ot yourself, the actual documentation is the Blueprints with comments itself. Most of the comments should make sense and put you in the right way. I think the easiest way to start extending it is, what do you want to do? Then i could just point you to the right directions.
Please also note that i usually answer to any emails i get and try to help people as good as i can, even if its not directly related to the asset.
Cheers,