is it possible in a smart way to make Moodle syncing users to Joomla. We about 1000 users which we would like to sync to Joomla... do we need to change authentication method? would that force a sync?
No, that would not force a sync. To sync Moodle users to Joomla you need to do it in batches from Joomdle users screen in the backend.
Please note that this will set new passwords, as we cannot transfer Moodle password to Joomla.