Since you are going for a shorter trip, I would recommend making reservations in advance; a few weeks to a month should be sufficient unless you are going during a holiday. As for "couples time," I think there are only a few choices, but I admit I have not tried any of them. My other half has no interest in pampering, unfortunately!
I have tried conventional treatments (mani/pedi and messages) and somewhat unconventional treatments (hot stone therapy, aromatherapy whirlpool baths, and sugar scrubs.) The only bad experience I had was an overly "enthusiastic" message therapist who overworked some areas; my tookus and shoulders hurt for a few days. Live and learn! Other than that everything else was great.
I would suggest that if you are considering a treatment with which you are not familiar, that you ask a lot of questions before booking. Sitting there wondering what is going on or about to happen does not lead to full relaxation in my book. I need to know what to expect or I do not feel comfortable, and that is the point afterall!
Other than that, just enjoy the pampering!
Blahnde