Ruby, an overnight as a first booking is one hell of a tall order as it is and an overnight sub booking could turn out to be an absolute nightmare - have you discussed things like limits, boundaries, exactly how the booking is going to go including how much down time you're going to get?
Assuming this man isn't a fantasist (and people who ask for long, expensive bookings as a first appointment often are, although by no means all; make sure that you're aware of local 'going rates' for overnights though, particularly since you're offering niche services which may well mean a few days off afterwards), then meeting him in a bar really isn't a good idea, for starters. You need to check that everything is OK with the place you're staying so that you can tell your security buddy and confirm that's where you'll be, plus you need to be paid at the start which is harder to do in a public place as you need to count your fee and make sure it's correct.
I can't add much more because my real advice would be not to do it, and to cut your teeth on some shorter/textbook type prossie stuff, but the main points are to make sure you have a security buddy who knows exactly where you are and who you will agree to check in with, make sure everybody understands what will and will not be happening during the booking time and most of all, that you're getting a fair fee for this, since I suspect you won't be.
Oh, and if you haven't already, do read the
main SAAFE site 
.
EDIT: Crossed posts with Ian, but what Ian said.