With 20+ FOH staff, I would like to be able to track who has taken bookings/updated details etc.

However, having to enter an email address and password each time is too time-consuming, versus a simple pin number system (like our till login uses).

Once complete, could the system log the user out to a home screen, ready for the next member of staff?

Yes exactly that. A simple number like the POS. The diary could be open to be viewed but as soon as BOOK was clicked, a simple pin code would be required.