How to work with nested objects in MongoDB + Yii2?

Question

Yii

I have a collection "event" with the following structure:

_id, ... 
  games: [
    {
      _id, ...
      sides: [
        {
          _id, ...
          units: [{_id, ...}, ...]
        }, ...
      ]
    }, ...
  ]
}

I'm currently learning how to work with Yii2 and mongoDB. For this collection, I made a standard MVC via CRUD and a model generator. I manually made a conclusion in kartik/grid/gridview of nested arrays of objects through ArrayDataProvider, but naturally editing does not work now and the following questions have arisen:
1. What structure of the collection will be correct and more convenient in terms of working with it, when you need to frequently change the values ​​of the fields of nested objects ( games, sides, units)?
2. With the current structure, is it possible to make queries knowing only, for example, units._id?
3. If so, what is the best way to implement this in the model, when, for example, it is necessary to change only units._id[name]?
4. What would you advise to read about mongoDB, in addition to documentation and general development manuals?
Thanks in advance for answering questions!