Are you doing it to actually build a business or sharpen your skills? If former, start with Firebase and pivot when you have a proven market. If latter, starting with both backend and frontend is a no brainer.

But I'll never underplay the importance of having both backend and frontend skills -

- It's a core set of skills which will pay off multiple times in the future. - Easier to pay off the tech debt in the long run. People seriously underestimate the capabilites of postgresql + ruby on rails/express + a frontend like react. - It's much better to be dealing with the problems of an open source software than a proprietary one. - Learning how everything works together - how to frontend is wired to the backend and how the backend models the data in the database and how to deploy all of it together - is invaluable. - Almost always cheaper than proprietary solutions.

Learning between the two is a matter of tradeoffs. If time is of essence, then you probably should choose things which are easier to learn and manage. However, in the long run, proprietary solutions rarely beat the combination of postgresql + rails/node + react.