I may be singing the same old song again, but I still think the documentation to set up a dev setup is just not complete enough to intrigue developers that are not full-time Java and maven cracks.
Have you checked https://dev.xwiki.org/xwiki/bin/view/Community/Contributing and specifically https://dev.xwiki.org/xwiki/bin/view/Community/Contributing#HContributeCode
This leads you to the Onboarding area:
https://dev.xwiki.org/xwiki/bin/view/Onboarding/