Elasticsearch word frequency and relations
To get term frequencies you could use term vectors. However, you would first have to store them and second, you can retrieve them only for a given document.
As far as I know, it's not possible to aggregate over term vectors.
Maybe you could achieve some of what you want using scripted fields. But then again, Groovy is currently disfavoured because of security issues and aggregating over scripted fields is potentially quite slow.
By the way, similar questions have been asked before: