Aws infra recommendation

Project: Need AWS infra recommendation

Description:  A ios/android app where a user signs up, fills out a survey and submits photos to be printed.

The flow needs to be:
1.    User sends 9 images
2.    Server merges these images into a 3x3 grid and saves them to s3
3.
Server then asks a service for a matching set of 9 images (based on the user filled out survey)
4.    Server merges these images and creates another 3x3 grid and saves them to s3

My initial thoughts were to have 1 rails server to handle everything.

There will be an extra rails server with a webapp to administrate these merged images. The idea is to be able to download batches of them and manage some state (mark them printed, etc).

I need is advice on what would a micro services setup would look like? The cost to set it up, an approximate monthly cost

What I think It would be needed:
1.    Server for Rails
2.    Server for image processing
3.
API Server (receives user id and returns 9 image urls – based on the user survey)
4.    DB
5.    S3

Let me know if I’m completely wrong, or how would you set it up.