Periwinkle, if you can see a photo of the pool, look at and count the tiles along the outside edge bordering the pool proper...they are approx. 1 ft. long and thus you can almost exactly know how long and wide they are. Can't help with the depth, though!
Enjoy St John. We started out renting in Cruz Bay but moved to Coral Bay for the peace and quiet once they started building that monolith that now overlooks the entire town. The most incredible villa we ever rented was Island Horizons in Coral Bay, esp. if you want to cook in. The view down island at night to all the other islands was lovely. The only thing I would have liked was a sunset view.

The 3 eateries I'd recommend in Coral Bay are Aqua Bistro, Shipwreck Landing and Miss Lucy's (esp. the jazz brunch on Sunday).

But wherever you rent, get out there and visit all the beaches.