Fork Mapping module or extend in theme?

I’m designing a collection in Omeka-S where many items may be related to a location. There are many locations, and many more items. Each item is associated with a location.

I am hoping to use DanielKM’s Archive Repertory module to create a logical structure for my files using the location-based item sets as the first level of the directory hierarchy.

This is all good except that I need to extend the Omeka-S mapping module so that item-sets can have explicit locations as map markers.

My questions for the forum :
Q1. Would there be anything wrong with this design overall that you would warn me about?
Q2. Should I fork and extend the Mapping module or include my extension in a my custom theme?
Q3. If anyone would like to sketch out a road map for which files are involved in adding location to item-sets I would be most grateful.

Thank you
–pbc