Im a bit late to the show, but I personally feel like you are heading down the wrong path. Unless you are trying to completely host locally, but for some reason want your backups in the cloud, and not simply on separate local server, you are mixing your design for seemingly no reason. If you are hosting locally, you should back up to a separate local instance.
If you indeed are cloud based, you SHOULD NOT be hosting a DB separately. Since you specified S3, you are using AWS, and you should rather use RDS managed mySQL and should use the snapshot feature built in. ref