We are growing SP2013 enterprise into many site collections and databases to help manage capacity, SLA, performance, etc.
Separating a large collection for one business unit presents a problem of getting search results from 5 site collections, but not the others.
It seems I can create a search source using the Path parameter for each of the 5 site collections. Which seems to obvious to be true.
Am I right in using this technique, or are there other options?
Mike B
Search is the best option to view content across site collections.  As you stated you can create a custom result source  and use the path parameter.  That is the way that I have done this in the past and have had success.