Monetisation first. You should start from there. Even further: take in serious consideration only ideas in which the monetisation works in the core part as an acceptable element of the core gameplay.
If you glue it on at a later stage, it will feel detached and player's will feel that you are there only to rip them off.
It's really a very fine line. If you cross it, your monetisation will drop dramatically. This is something you should find and test before any global reach.
You might have a great game with good monetisation foundation, but you haven't found the sweet spot if there is one.
Often senior and very expert game makers start their own company, make a great game, but the monetisation is low if non-existentent. It can be related to previous matter, but also the monetisation is not present.
In other words, the player is never offered any purchases. The player just plays the game and runs into a dead end.
From time to time you can
You have to respect your player and give them a feeling that the game has value for them and is created with love and respect. They will spot rip-offs miles away. This is also the reason why huge game with high production values do so much better and it is difficult for small games to monetise.
Price points can make a huge difference. You really need to try these out before going global.
It will be easy to drop the prises, but it will be hard to raise them without getting angry players.