1. Apple Developer Program: this is yearly membership cost about USD99 to publish app on iOS App Store, Mac App Store and also Apple TV Store. With this account you can access iTunes Connect, the portal that manage your app on the App Store. Link. If you want to register under a business entity you also need DUNS number.
2. Knowledge of Managing App: at least you must know how to upload the app to App Store and using iTunes Connect, creating app details and much more. You may want to develop by your self, hire people, outsource the project or even buy a source code. Whatever your path it's quite important to know the publishing side of the app.
3. Macintosh computer: It is a must for developing apps for iOS platform, it's not only a great computer for developing but essential to create the app as the tools only on Macintosh platform. At least you need Xcode program to create and upload to the App Store. If you out source the project, you might not need it.
4. Devices: You may need at least one device that run iOS, preferably the latest one, so you can test latest features. Don't care much on the previous generation of device, because in the future people gonna use the latest hardware, and as developer it's important to think for the future. Well, if you do have more resources, yes, definitely have older devices and support them too. You may also ask outsourcer to test the app if you outsource the project.
1. Android Developer Program: this cost about USD25 for lifetime. This will give access to Android Console.
2. Knowledge of Managing Apps: know how to manage the apps on Android Console publishing platform.
3. PC/Mac: Both platform support development for Android. The essential program to create Android apps is Android Studio. Link
4. Devices: The best development phases are testing where you make sure the app run smoothly and not crashing on the actual devices. You may use Google phone like Nexus, or use the common Android smartphone like from Samsung. You may also want to try on cheaper Android too.
So these are essential things to need to get started with mobile (iOS + Android) business. Well, there are many ways to learn, buy and outsource the apps. What you need to do is to manage the apps and make sure it runs well. Marketing the apps also important to make sure many people know about your apps.
Here are some tips on app marketing stratergy, hope it helps.