How do I track those relationships?
Do you need to?
I mean that the main questions to ask yourself are about the What and then think about the How.
- So what are my users going to search for?
- What kind of information do they need to search for those entities?
That's IMHO the main major questions to ask before trying to think about the implementation. I'm used to say at conferences that forgetting about all the stuff you learned at school about Relational Databases is one of the hardest thing to do when you want to play with Document Oriented systems. It's really not that easy to change your mindset, specifically when you did that for years. At least, that was my experience when I introduced Elasticsearch and CouchDB at $job-1.
I tried to explain my thoughts there:
I hope this can help.