Firestore creating a representation of a order form - date

Question

I'm new at firebase/firestore. Appreciate your thoughts on this.
I'm trying to create an order form using Firestore.
I was wondering:
Do I need to create a YEAR, MONTH, DATE of collections and documents just to save all the order forms ?
This felt redundant to me, otherwise a lot of databases in Firestore will require a lot of collections and documents of dates!
E.g.:
(CAPS is Collection, bracketed are the documents)
YEAR (2018) -> MONTH (Jan, Feb, Mar, etc)
JAN -> 1 (order #1, order #2, order #3, etc)
JAN -> 2 (order #1, order #2, etc...)
Or just a simple time stamp on each document of order form - and then if I want to look up say for the month of January, is there a search query to look up all the documents in a specific month? or date?
And as order forms go, the user can enter as many items as possible. Is it correct to have each item stored as a new document? Therefore possibly creating 100+ documents per collection of order form.
E.g.:
order 1 collection - banana document, apple document, orange document

Answer 1

There is no single best data model. It all depends on the use-cases of your app. For a general introduction to this domain, I recommend reading NoSQL data modeling.
But in Firestore having a collection with many documents is not a concern. The database was made to scale to almost any number of documents.
You'll indeed want to store a timestamp in each order. The best way for this is like to use a server-side timestamp. You can then query for orders in a given date range with a query like this:
var now = new Date();
var yesterday = new Date(Date.now() - 24*60*60*1000);
ordersRef.where("timestamp", ">=", yesterday).where("timestamp", "<=", now)
Or
ordersRef.where("timestamp", ">=", "2017-01-01").where("timestamp", "<=", "2017-12-31")
For more examples, see the Firestore documentation on queries.