Given your experience, it should be extremely simple, especially if all you want to do is drop NginX infront of your NodeJS server. All you have to do is install it and add a line in the config that points traffic to your NodeJs instance. Btw often times people use Nginx as SSL termination and use http to the backend (if on the same instance).

Let's Encrypt can automatically add lines to the nginx config that enable SSL, but in some cases it doesn't work properly and the config is malformed. In any case not hard to fix.