Implementing data upload and read microservices project

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Java

Spring.NET

Spring

springboot

, +

I'm new to Micro-services architecture, I'm to develop a project using spring boot that gets data from API and stores that data into PostgreSQL db then computes and gets the sum of the data uploaded and sends that data into another database MongoDB then reading these computed results from MongoDB to front-end application. now my question is how many services should I have in order to accomplish this objective without forgetting authentication to all users that will be interacting with the application.

What I have tried:

developing department service and user service then performing inter-services call.


Any suggestions will be much appreciated.