Welcome to the wonderful world of extending Sling. Refer to these pages to find out how we envision the extension of Sling and how to do it.
See also Developing for Sling on the Sling Wiki, which has more information on specific topics.
Look here for more information on developper support when your are using Sling to build your own applications.
Sling is using Apache Maven 3 as its build system. Over time we have created a number of Maven 3 plugins and gathered a whole range of knowledge about using Maven.
Last but not least, here is some more information on how we ourselves are working on Sling