Organizing Your Photos by Peter Krough is a good source for drilling down into managing your images with Lightroom. The concept applies to succeeding versions of Lightroom. So, although this book was initially written for Lightroom 5, it is relevant today.
Regarding your desire to restrict images to a single collection, perhaps a collection is not the way to go, but to create another folder and move subject images to that folder. i.e. utilize folders not collections.
