Try starting FaceTime then go to the FaceTime menu and select Preferences. If you have never used FaceTime before you will need to sign in with your Apple ID. You can then clear the tick against Enable this account. If you don't use FaceTime on the Mac then sign out. This should stop the FaceTime message on Startup.
As for iCloud, there are lots of suggestions above. iCloud is used in so many places it is hard to find them all, FaceTime preferences is an example, but if you do sign out everywhere then you should find the messages go away once you sign in again.
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