[bobkazamakis]

Focus on how you wish to share your code, and what features you need to deliver. If you're developing multiple small applications, it might make sense to build some re-useable core libraries after you've assembled the first one (do it too early and you'll be trying to 'bake an apple pie from scratch').

Need variations and reuseble front-end components? Package em up and take advantage of es modules.

Need to share common business logic? Package it up and share ruby modules.

At a certain point, you'll find domain boundaries within these, and be able to split them based on their use (delegate authN/Z to an sso "service").

Microservices (when not taken to an extreme) help build a pathway to re-useable code, much like TDD helps you write code that doesn't abuse side-effects, static classes, etc.

Don't split them out too early or you'll spend all your time keeping all these dependencies in parity - don't want to serve a raw steak or a burnt one.