My biggest piece of advice is make sure you have “One Source of Truth” for all your user data. Since requesters can be created in freshservice simply by having an email sent to your support email address using an email address that doesn’t already exist for a requester, it can get out of hand fairly quickly. So I would suggest making sure you either whitelist only the email domains that you want emailing your service desk, or make sure you have practices in place to manage your user data.
Best of luck with your implementation. Freshservice is powerful, so be sure to come back and reference this community as you build out your service desk. A wealth of knowledge here :)
Take care.