On our first visit to CSA we stayed on a 3rd floor and loved it---the view, the privacy, etc. We are going back in April and have booked a BFVS and hopefully we will be able to get a room on that floor again. Our opinion is that the stairs are no big deal.
The stairs are going to depend on you...your physical ability. If you are able to climb three flights of stairs without difficulty they won't bother you at all. If three flights of stairs nearly kill you, well then it's gonna be a problem for YOU.
As for the room, we had a first floor room and loved the ability to walk right out onto the beach. But there are folks that love those second and third floor rooms for the privacy and I can understand why. On the first floor people walking by do what human nature guides them to do...look at the stuff around them which includes you on your verandah or inside your room. Not like they walk up to the windows and peek in but as they walk by they naturally look that direction. Even after having a first floor room and loving it I can see benefits to those upper floor rooms. Like anything in life there are pluses and minuses, no matter which room you get you are going to LOVE CSA!!!
We were in a third floor room last time and I'll admit it was a little rough going up them (I'm not in great shape!) -- especially after a day of drinking. It certainly makes you plan your day a bit better because you don't want to have to "run back up" to the room very often. With that said, though, I'm not sure I'd like a ground floor room as there is no privacy at all. The paths through the resort pass right in front of them. Some people don't mind that, but when I'm in my room, I want privacy. We're going to be back May 2 - 12 and really hope we get a second or third floor room! Of course, if we do get a ground floor, I'm sure I'll enjoy the advantages of it! Bottom line... you'll have a great time, no matter what. There are no worries in Jamaica!