Hello,

You can install Node.js and PostgreSQL on any droplet. I could suggest starting with either CentOS or Ubuntu.

You could start with a smaller droplet and upgrade whenever needed. I would recommend monitoring your resources usage and also maybe running some stress tests to see how your app performs depending on different load.

I would recommend having a look at this tutorial here on how to get started with load testing:

https://www.digitalocean.com/community/tutorials/an-introduction-to-load-testing

Regards,
Bobby