@Caoimhe_Maguire, hi and welcome to the community 
! What you’ve described seems similar to how the app can work, and is actually a common use-case we’ve seen. We put together a topic on this in our Producer Series:
From this topic, you’ll see that you can create users like “Freelancer 1”, “Freelancer 2”, etc, place them in the appropriate department, and the keep those users disabled until they are hired (you can use your email address or another as a palceholder). Then, once you are hire that person and they become “real”, you can edit their profile/email/etc and send them a Welcome email. But, while they’re a disabled account, you can filter by that in the Crew Planning Advanced Filter. Does this type of workflow suit what you’re after?
Here’s the full series, in case you’re interested in exploring more Producer workflows: Want to learn how to be a producer power user?