Your wallet.keys
file should be perfectly safe in the cloud as long as your passphrase to unlock it remains secure.
You are correct about the use of Chacha8Chacha8 to protect the file.
As long as the file remains encrypted, wallet.keys
will not leak any data. Renaming it should not be a problem, but to be safe I would keep a backup of the original file (prior to the name change) until you confirm the renamed file still opens properly with your passphrase.