Jayne, perhaps I'm being sceptical, but I find it odd that you had to google to find out how many people the guest was bringing with him. They're students, which - unfortunately - already raises a red flag for me. 🙂 (I live in a university town. 🙂 )
Have you asked the potential guest why he/she chose your accommodation?
Has the person indicated the reason for visiting? Is it over a weekend?
How long do they intend to stay?
I note that you have a 'no smoking' house rule. Do you think that 7 students would adhere to that?
Your place looks lovely, and doesn't seem to me to be well suited to a large group of young people who might be intending to party for a couple of days. Of course, I'm only presenting a worst-case scenario. But in your shoes, I'd seriously re-consider the pre-approval.
Others, of course, may feel differently. 🙂