Have you considered that you may optimize excessively and way too early? People who would buy your product do not care whether it's serverless or not.

If people like product and it sells well, you will have time and money to refactor your product (I would still think twice before doing so).

Consider this: > remoteok.io is a single PHP file called "index.php" generating $2,342.04 in a day. No frameworks. No libraries.

If you want to start quickly with app that has signup and pay for content, consider this open source app: https://github.com/builderbook/builderbook I am a co-author.

If you really need passwordless-like flow, check out: https://www.npmjs.com/package/passwordless