How to keep things well structured
If you start learning from the feedback you obtain through interviews or metrics, it is very likely that the flow or structure of your app will change. As business requirements change often, ad hoc changes need to be made. This requires you to refactor the code of your app. That is something that most developers consider to be important, but in reality it can be easily forgotten or it is never done, simply because there is not enough time for it. Sometimes, refactoring is considered to make the app unstable. However, do not let your technical debt become too large.
Technical debt or even spaghetti code can be the result if you understand underlying process insufficiently, or when you do not allocate enough time for development. In case a startup company has only business-oriented skills, it may have outsourced the development or it may have hired some third party to do the job. If that is the case, there is little to no insight into the technical structure of an app. I strongly recommend you to do most of the development yourself. If you do own a startup with no technical cofounder on-board, then stop reading and find one first! There are many meetups and websites where you can meet somebody (for a cofounder or another role) with the skills that you are looking for. Take a look at these websites: https://angel.co/ and https://cofounderslab.com/.
It is important to keep things, and your code in particular, well structured. Design patterns and a number of disciplines could help you to achieve building apps for Android and for iOS. It is true that Android Studio is offering much more functionality for refactoring purposes, and that using Xcode refactoring requires some extra effort. Nevertheless, refactoring is equally important for both platforms.