the easiest way is to use subprojects in gradle. (Structuring and Building a Software Component with Gradle ). Currently we have one root directory and two subproject (core and example). Today I create a new subproject server on my branch network. If the root project is build, all subproject are build if wanted. To integrate a new subporject is really easy. It completely described in the gradle documentation.
But I am sure the challenge is to split up the source in a smart way. Let my know, if you have commited your first branch version. Than I am able to help you.