I'm so excited for you two!
I think we all tend to do the same thing when we're anticipating a new experience -- our minds go crazy thinking about "what if ...(fill in the blank 1,000 times over)." Speed and I definately did that before we went to the club for the first time! The hardest thing for us is to say to ourselves "hey relax! We're totally fine!"
You definately have the right attitude: go to have fun with each other, be upfront and honest with others, and don't expect anything else. Naked hot tub? Meh, whether you do it or not, it won't be your last opportunity to try it. I love your "we'll see how it goes" approach to the vacation. Have fun together, because that's all that matters. You'll probably meet some very nice people, and you'll FOR SURE have some great sex (with each other). Sounds like a great time to me! Please come back and tell us about it.
Happy and safe travels,
Trixie
PS Now, about this "g-string" bathing suit of yours....