how to plan for scaling-architecture of a single-droplet Digital Ocean app

I'm about to launch a nodejs-mongodb app on a Digital Ocean (DO) single droplet. I'm here to make sure if I'm reasoning correctly on how to add droplets in future for scaling against load, if any.

I'm going to:

1. setup Nginx, MongoDB, Nodejs app, all on a single droplet of DO.
2. create an image of the app into DockerHub, further launch app from the droplet and wait until it brings load.
3. Then create a Rancher network with Nginx and app-hosting droplets,
4. finally, switch off the Nginx and app from the initial droplet, replace it by the Rancher network app-hosts. The initial droplet will be First MongoDb droplet-server.
5. further, when necessary, to add MongoDB droplets and sharding to have a cluster of MongoDB, to add app-hosting droplets in the Rancher network.

Please let me know if these steps are what I could rely to, or where else I should look.

via Adrian Dain