Update: had a wonderful evening last night. He was a gentleman! And he handled the payment very well. It was wrapped in a hotel evaluation form :-). I counted the money in the ladies room and it was all there. So it all worked out fine. Thanks for the advice from you girls!!!
Glad it went well in the end!
For future reference though, it's normally recommended that all the initial meeting/payment stuff takes place in private - that way you can count the money in front of the client (so you can't be accused of pocketing any on the sly if it does turn out to be short), plus making sure that the hotel room is the right one and everything's OK for where you'll be going later means you can do your call to your security buddy clearly in front of him too.
Not to mention the fact that you don't know what a new client looks like - if for whatever reason he'd bottled it or decided to be an arsehole, you could be hanging around a hotel lobby feeling like a pillock while he (and possibly some mates, depending on how thorough your security checks are) got a good look at you. Not fun.