@Tamsin4 "I have only ever suggested making contact outside the platform for long bookings so I can get a sense of the guests and answer any questions they may have with more ease..."
Why is it easier to do that on social media than through the Airbnb messaging? As a home-share host I exchange quite a few messages with guests so we can get a sense of each other.
One thing you should be aware of, though, is that Airbnb isn't a good choice for long-term bookings, even though they encourage them. They only guarantee the first month's payment, if a guest reneges on the following month's payment it is then on you to evict them, but by that point the guest has been there long enough to fall under landlord/tenant laws.
Also Airbnb so-called security deposit is bogus. And their "verification" process is no assurance of anything.
So if you are going to take long-term bookings, it's a better idea to have the guest book for 28 days through Airbnb, then after their booking comes to an end, you can make private arrangements with the guest, with a legal lease of some kind for the following months.
You wouldn't want to suggest this through Airbnb messaging, I would just say that you don't rent for longer than 28 days for the initial booking, to make sure that the guest is a good fit for your place, and if it turns out to be and they want to extend, that would be discussed after they have been in residence for a few weeks.