2
You might want to look at WgGallery (https://github.com/ggoffy/wggallery) - it uses some of the XMF features, PHP namespaces, uses the "common" admin GUI, etc.
It would be a good starting point to help you understand how to implement some of the newer XOOPS 2.5.x features. After that you can browse some of the recently edited modules in the GitHub modules repositories to see other examples.