Set up your environment carefully: It's important to have one canonical source of truth per environment, per platform. (i.e. iOS Development, iOS Testflight, iOS Production, ditto Android.) Every time you build, your config should propagate values from one input source (per platform) to either Java/JavaScript or Objective-C/JavaScript. Here's what we did for Android and here's what we did for iOS. I don't doubt that you can do better. Please do better. But you can't say that we didn't have one canonical source of truth that worked very simply and effectively throughout the development process.
Don't wait until the end to develop Android and iOS concurrently: Even if you're not actively focusing on both platforms, don't assume that "RN is cross platform… we can develop iOS and flip the Android switch when we'r