I haven't been in this hobby for all that long and I certantly don'tknow all the answers but it seems to me that there are questions that it is unwise to ask, Some have been discussed ad infinitum. like lowering the fee and very personal info like where they live, are they married. etc. If you get to know them through multilple visits they will tell you. One that I think is a poor question unless you really know the lady is "did you cum" Chances are she wil lalways say , "of course", just to stroke your ego. If she volunteers that, she stiill may be fakeing it.But there is a better chance it will be the truth.

dinner/lunch OTC?, Can I date you for fun?, etc.

Unless she volunteers, questions about her non-professional life are strictly verboten....

What else can't we do? Are we allowed to LOOK at the gals when they open the door to let us in?

" Are you gaining weight " is always a no-no..

but here I one I don't think is one  "Is it in"

The truth of the matter is they don't really care and the honest answer isn't what they are looking for so Im forced to put on a happy smile and lie. Even if I answer what I like they still move ahead to with whatever they want which usually means they are trying to push past the massage service they have paid for.  I know every provider says you give oral just as good as her side lesbian lover ; )  

-you're a fabulous lover
-your penis is beautiful & it's not too big or too small
-I've never/rarely/seldom felt like this
-I wish more of my clients were like you
-your touch/kisses/stroking/tongue are AMAZING
-nobuddy, has ever done that to me quite that way!
-I'll bet you were quite the tiger back in your day (I'm not now!?!?!?!)
-I'm having so much fun with you

They usually list the answers to questions they don't want asked. I see several ladies fairly regularly around the country. A few of them will have meals with me OTC ( offered by them) ,but with some of them it's not part of the deal.  
An interesting thing that I have found is that communicating respectfully usually gets respectful answers.

If UR nice, if I have the time, and if I"m hungry, Y NOT?
What's the worst thing that can happen?  I might say no?  Oh, the horror

Asking any of your questions in the manner you suggested is also a bit rude.

OTC, after a date with a provider. I was hungry, she was hungry. I asked, she accepted. We just walked across the street from the hotel. After dinner, she actually asked me back to the room to watch a movie with her. No sex. Just hanging out watching a movie, and talking. She was lonely wanted some company. On the other hand, one week prior, a provider seemed to be giving me continuous hints that she wanted me to ask her to dinner and when I did, she turned me down. Left me confused, but No harm no foul. Like you said, sometimes you are hungry and the worst that can happen is you say no. And like GaG says a lot has to do with how it's asked.

Benihana's is to Japanese food what the Olive Garden is to Italian food

...they asked me sometimes I ask them. Sometimes they say not today but next time. Next time they followed through.  

Did you not know the salad and breadsticks are free

I have had lots of dinners OTC with an ATF. It became a regular thing depending on the time of our meeting and other commitments.With another lady we did fun things  OTC before a regular session. These activities were with providers I have seen numerous times.
These activities have been between friends. Today I had a 2 hour lunch with a provider who retired over a year ago.

Hey, come on, What have you got against Warthogs? lol They may be not too pretty, but roasted they are one of the best eating African wild animals.

Is the next session free? What's your real name? Can I have a rain check on your special? Do you have a volume discount? How many lovers have you had in your life? Do you wish we'd met in real life? Why did you become an escort? I know it's been a year, but can I have a reference? Can we do lunch and a movie? How old do you think I look? Why don't you quit the hobby? What celebrities have you seen?

Well it was late, and Red Lobster was closed.

It was convenient because:  
#1, they were right across the street from the hotel, and
#2, they were open at 10:30 on a Sunday night.  
We actually walked to the hotel front desk together and asked for a decent restaurant close by, and that was the referral. Hey wait, wasn't that breaking all kinds of TER rules about hiding and not being seen in hotels? Lol

And, "are you lonely sometimes"?   My ATF has already answered those, voluntarily on her own.  

True experienced, a lady asked me once, questions came out like this...
How old are you? your race? do you use Meds? are you a magnum gold? are you circumcise? Took me a while to figure out how to responds......

One of the best songs of my generation.

How about this one...Maybe this not to bad to asked but here it goes. You're 69 years old? do you still have any teeth? do you wear dentures or dental appliances?