How long is normal for a provider to respond to an request for an appointment?  
It is really hard to say, some of us have other obligations, family or other affairs to take care of. My reply time is typically quite fast (1-2 hours) unless I am either in school or meeting someone. I have an assistant so whether I am available by email or not, she can be reached right away. I would say give ladies 24 hours.

Would a provider let you know if she does not wish to meet with you?
Unfortunately you will find that some providers won't respond, I try to have the channels of communication open and give you a reason or try to ask you for all the screening info or additional should it be necessary but sometimes we are victims of aggression and verbal abuse if we decline for various reasons so, typically to avoid those confrontations, we just do not address the issues. (bad references, blacklists, age, character, inappropriate questions or language on emails etc). I am not saying this is your case but please keep this in mind.

* What would be considered acceptable as an Upscale Hotel?  
My reasoning is, I will never go to a place where I will not hold incall. I have been to numerous boutique hotels here in Miami, but please let the lady know in advance whether the elevator is keyed or where the elevator is period, the only downside about those hotels is that the front desk can be relatively small and close to the elevator so you wouldn't want her to look lost.  
Please have a water ready for the lady, I know it is a strange remark but it is a nice touch.
Good luck!