What are the things I should do before deployment of my NodeJS application?

Currently, we are working on a social media type application. This application will have some vigorous calculations at backend, bulk email and bulk sms will be send to users. We are using MongoDB, NodeJS, ExpressJS, AWS. I have added cluster in it. And right now there is nothing extra(like nginx, appache, cloud monitor,etc) we did for production deployment. We just made application (at development stage). Please guide me to make my app production ready( as our user base is almost ready, we will be having more than 15,000 users by December,2017). And it would be great we you could tell me the way to calculate the no. Of servers, CPUs we will be needing in future. Thanks in advance.