If I store something on iCloud?

Depends what it is. If it's photos then no it's not safe. You'll lose them. If you want to get photos off your phone but still have them, you need to download them to a computer, or upload them to an online storage facility like Google Photos or Dropbox. iCloud is more for synching info across devices than storage.

Yes Google Drive and Google Photos. You can delete any app off your phone and reinstall it again. If it was a paid app you wouldn’t have to pay again. Or you can use the Offload feature to delete the app but retain its data.