You are so right that monetisation needs to be thought about from day 1. I wish I had seen this article years ago! I learned this the hard way when we starting monetizing our features on our dating app that were previously free. The users revolted en masse with 1-star scathing reviews, which did irreparable harm to our user acquisition efforts and the traffic plummeted and never recovered as a result.
Lesson learned: Never start charging for features that users are used to getting for free.
I go into more detail about this painful lesson in my new book — Explosive Growth.