I try not to care, point of RN is that it’s cross-platform so ideally I never have to have any platform-specific code. I write once and check every so often for both; if these is an issue (open paths of SVGs causing rendering issues on IOS for example) I look for a workaround, but normally no issue. I would not develop sequentially, seems to defeat the point slightly. For development, I normally hook up a phone for Android and just use the XCode emulator for IOS. Android emulator is garbage and takes up insane amounts of space, so I avoid that if possible. Deployment means XCode setup for IOS, which normally takes a little fiddling; Android is much easier, but that’s not really a development concern per se
I am also on a Mac with little HD space, so developing with Expo is much, much easier but not applicable most of the time due to needing native packages for the apps I work on. So XCode, Android Studio, no Android emulator.