Your single or separate doc design completly depends on your applicetion. If you have an app that will need all data in same time (i.e. display all account info in some table) you should use “single doc” approach - because you’ll get needed data with less requests to database. If you have an app that needs different parts of data in different cases - you should divide that “parts” and store them in separate docs. If you use “single doc” approach in this way, you’ll get a large data transfer overhead, you’ll transfer large amount of useless data. But when you need “all” data, you’ll need more than one request to gather it.
Also if you have some parts in that doc which can change in differrent places at the same time, yoou should also try to divide that parts to multiple docs.