Firestore data modeling

Question

I am creating a new Firestore database and am new to NoSQL. I am creating an application where I would need 4 root collections. Users, teams, challenges, and tournaments. Users need to join teams. Admins need to create challenges and tournaments. Tournaments need challenges and participants. I was wondering how this could be modeled the best in Firestore. This is what it looks like in JSON format so far:

{
  "users": {
    "uid": "user_id",
    "firstName": "John",
    "lastName": "Doe"
  },
  "teams": {
    "members": {
      "user_id": {
        "uid": "user_id",
        "firstName": "John",
        "lastName": "Doe"
      }
    },
    "teamName": "Team X",
    "teamPhoto": "url"
  },
  "challenges": {
    "doc1": {
      "challengeName": "name",
      "challengeDescription": "description"
    }
  },
  "tournaments": {
    "selectedChallenges": [
      {
        "challenge_doc1": {
          "challengeName": "name",
          "challengeDescription": "description"
        }
      }
    ],
    "tournamentName": "name"
  }
}