Don't worry about all that security / docker with a MVP, you can deal with that once you know your project is solving a problem and you need to scale.

My personal recommendation is a small VM in Google Cloud for the app and another small managed postgres server (backups automated). GCloud is easier to get started with and they automatically migrate your app VM if there are hardware problems. This would run you less than $50 (~30 ballpark) per month. The other consideration is https (mainly for not appearing dangerous in the browser).

(Boycotting AWS)