What is best way to using Elastic search for searching (Via Server vs Direct Java Client)?

I am new to Elasticsearch. I want to store documents of products details. Now I am using Mongodb as my database and nodejs server. But Mongodb does not have good search functionalities like Elasticsearch.

So I am thinking of shifting to ES. But I have few doubts as stated below please suggest me what should I do. Any suggestion will be appreciated.

1. Should I use MongoDb as my primary database for storing documents and ES as secondary database just for doing efficient search. Or Should I make ES as my only database for storing documents and searching.

2. Does using both will be good for future or it will make thing difficult to manage. I have also read that ES in not a good choice for main database as it sometimes loses write operation.

3. Should I make a server in nodejs to perform ES operations for doing any complex search or GET, PUT using rest api or should I do it directly implement it in java .

(Note I am making a android app so should I use TransportClient and Interact with Elasticsearch directly or I should first send a GET request from android side to my server and my nodejs server will interact with ES and send response to my android app).

4. Other than search part is ES performs as good as MondoDb in terms of Database.

   Thanks in advance.

via Bhupendra Singh Chauhan