In reality, collecting data about WiFi users is a nuisance. It has to be looked after, protected from leaks, GDPR compliance, etc. Really, what are the benefits?
Attempts to harvest email addresses makes users uncomfortable. Hotels have the contact details of guests already. If there is a data breach, the hotel/motel will come out of it with a diminished reputation. Consider using a splash page, with appropriate disclaimers and setting up policies to stop access to inappropriate sites such as peer-to-peer, and deliberately recording as little as possible about users.