I'm developing apps with Cordova, but I have more fundamental questions to ask so bear with me:

1. For new apps on Google Play, I heard that you can only use FCM. I would like a double check on this.
2. From fiddling around, I get the impression that that Android devices which support FCM has got to be API Level 24 or later. Is that true?
3. If 2 is true, that means to support older devices, I need to use the same old GCM api on the clients. So client code would be written as they were connecting to GCM. Is that correct?
4. Then I can just write all codes for Android as if connecting to GCM?

Currently I have trouble getting Cordova plugin for FCM to compile and working correctly. I am hoping I can just use the GCM plugin on the phone devices.