Good to hear that! About the upgrades, I think everyone is dealing with the same situation. To avoid installing Crashlytics each time, you could try to install it through CocoaPods , so after you upgrade RN you can run pod install and that should be it.
While upgrading RN your AppDelegate.m will still be overridden because you’ve made changes on it but I suggest you to check if the new version of the file have changed because it rarely happens. If that’s the case you could copy/paste the old version of the entire file or simply do not overwite it.