Android first, or Android and iOS together?
Many businesses start with Android because most of their customers or staff use it. That is a sensible launch order, but it does not need a separate build later. Every package is written in Flutter, so the same codebase produces the iOS app as well. Choosing Android first is a decision about where you publish first, not a reason to pay for the app twice.
A native Kotlin build is still the right call for a small number of apps that lean heavily on Android-specific system features. If your idea is one of them, I will tell you during scoping and quote it accordingly.