Now you've got your hands on the how and why to use ads, IAP, leaderboards, and achievements, and know how easy the hard stuff becomes when you use Unreal Engine to process them.

While you have already got the core elements of monetizing an iOS game, before you move forward to the next chapter and start optimizing your game's performance, I would suggest you read some articles on the monetization science, as showing ads or adding IAP, or even achievements are just the tools and methods to monetize, but to make a successful monetization you've got to use these features at certain points during the gameplay.