Does Rsync after copy only send the differences between the folders, or does it copy the entire folder again since Rsync has never been implemented before on that folder?
rsync works by checking if a file exists, then if its checksum is not the same, then if parts of the file have the same checksum, then transmit the parts which have a different checksum (or, falling back to transmitting the entire file if it's missing or it's impossible to find a part which has a matching checksum on both sides). So if you have a file with the same name but completely different contents, it may be cheaper to transmit the whole file instead of the difference.
No state is kept outside of the file itself, so it does not matter whether you have used
rsync before. The contents in the file is the only thing that
rsync uses to decide what to transmit.
rsync can do both. If you do something like
rsync -auvz /some/directory remotehost:/destination
/some/directory will be copied recursively to
remotehost such that
/destination/directory will then exist. If you run the command again, only changes will be sent.
If you want files at the destination to be deleted if they no longer exist at the source, add the