WhatsApp and signal work fine without GCM/FCM, dunno about other apps but WhatsApp it's international standard so you are fine
you can get updates through their own app store AppGallery, but your paid apps are paid through Google, so don't expect them in order store, tying your money to Google ecosystem was bad idea in first place
you can get updates through their own app store AppGallery, but your paid apps are paid through Google, so don't expect them in order store, tying your money to Google ecosystem was bad idea in first place