I know a provider since 2012 and we have a good relationship. Yes I asked her and she said she considers me a friend. We both know each others real life details.  So, I'm thinking about taking her on vacation.  Maybe Key West or Sedona in winter for a few days. Am I making a really big mistake or not? Have you ever done this?

then you're most likely not ready to be going on vacation with a provider.  

If you have spent a few overnights with her, a few days is not that big a leap and you should be fine, BUT if you've never been with her more than an hour or two, a "few days" with the wrong person can feel like an eternity.

Go for it !,  you've known her for 8 years so there should be no major surprises.  You probably have had  to excuse yourself, in her presence to  
go to the bathroom.  You probably have even farted in each others presence.  And there certainly aren't any anatomical
surprises (like a cleverly concealed penis) to worry about.

She's still working, so you'll need to agree on a price up front and pay her way.

Given you have known her a long time and it appears you both consider each other friends beyond the P4P aspect, you might just try the direct approach.

Yes, there are no out of pocket costs for her, zero. If she wants to charge me a daily rate, that's fine. She has gone "back and forth" on that. She's not going to be my sex slave.... it's probably sex once a day. It's more like (if Key West).... sail boat sunset ride, jet skiing, swimming, just walking around shopping and people watching. She said she once was flown out to Vegas and was told to stay in the room all day which she did. I would consider that rude as hell.

If so, then go for it.

And if it took you eight years to just think about the concept,  I'd say you'll probably never be ready. You're making it a bigger deal than it really is

I do suspect that if you had to actually ask her if you are friends then you are most likely very "friendly" but not quite real friends. Do you still have paid sessions with her? If so, then you most definitely need to get the financial details out of the way early so that neither one of you feels "cheated" during or after the trip. You certainly don't want to ruin your relationship with her over a misunderstanding in this regard.

I wholeheartedly agreed.

Would you be the first one she would ask to go on her vacation? If the answer is no, then it's a business transaction for her. Don't make her ask for compensation,  generously offer her 3 to 5 times your normal arrangement per day.

What if he were number 2 on her list of people to go with?  Or what if he were number 10 on her list? She might actually enjoy the trip and NOT getting paid means she is not "on the clock" which means she doesn't have to be "on" the whole trip like she would if she was charging for it and this way she can just relax and enjoy the trip without having to worry about keeping her "customer" happy.

"Yes, there are no out of pocket costs for her, zero. If she wants to charge me a daily rate, that's fine. She has gone "back and forth" on that. She's not going to be my sex slave.... "

Well not EVERY situation is the same. Have a really good friend thats now happily married to a former long time provider. That relationship started out strictly "transactional"... Then became an "paid arrangement" as he really liked her beyond the client-provider sort of deal.  

If you've had some extended sessions and all was good, try a short vacation -- perhaps a long weekend in Sedona would be a good test.

I would love to see a woman's perspective on this.  I am in sales and occasionally  have to entertain customers. Its work even if I am at a Springsteen concert or sporting event.  

It really depends on the specifics of your relationship with her (As others have already mentioned).  You’ve been seeing her for awhile so I’m assuming there is a connection. My best advice is to just talk with her and be completely open with what you are thinking. The more she knows and the more open you are, the better chance that you’ll have a great time.

For me is a big risk to take many days with a random person. Can be a great sorprise or a complete disaster. So better have some date before to meet each other and see compatibility and if it's work or not.

cuts both ways.  I would never consider even booking an overnight with a provider I was seeing for the  first time, much less a multi-day vacation.   I have vacationed with a few providers, but they are ones I was a regular with for a long time and we were both very comfortable hanging together.  In a lo of ways, social time together can be a lot more demanding that sex time.

Have you done a few overnights with her?
Do you have a good chemistry?
If yes on both, then go! Don’t haggle about money ... and have a good time.
No amount of analyzing and planning can eliminate all risks ... just take a plunge and the odds are you two will make good memories out of it.
(Just since you mentioned, I have done a Sedona in winter on such a trip - it was an excellent memory!)

Yes I have done this with a few of my really nice clients and we just have a blast, the only thing I usually ask for is my own separate hotel room, its not because I wouldn't fall asleep with someone, or spend time with them, but usually I literally cannot fall asleep with someone I don't know, or potentially they snore, and if they snore I will want to die and won't really enjoy the vacation. So I always get my own room, plus then you can have some separate time and don't get completely sick of each other.

Is this a precursor to a relationship outside of the hobby, are you looking to keep it professional or just see where it goes?
I do not see a problem as long as you set the ground rules as to fees and expectations.  You obviously have a long-standing relationship and enjoy her company.  You just do not want to screw up the relationship you have and want to avoid creating expectations.  Ask her directly like you asked here.  See what she thinks about it and then go from there.  Good luck.