Icloud storage

Each Apple ID comes with 5 GB free iCloud storage (well, there is a subgroup who only get 1 GB). It's the same regardless of the size storage of your device but having a device with larger storage on the device may mean you will want to subscribe to more iCloud storage because of how device and iCloud storage interface. Click on this link to "Learn the difference between your device and iCloud storage, ways to manage your space, and where to buy more if you run out." --> https://support.apple.com/HT206504

If iCloud is full it won't let you add more things to it.

I don't know the the methods for transferring data from iPhone to Android. You may need to ask about that on an Android support web site.

To learn "How to back up your iPhone, iPad, and iPod touch" click here --> https://support.apple.com/HT203977

See the link about backing up to a computer.