We love Kiawah, and usually visit at least a couple of times a year.

My experience is that going through the resort, you cannot guarantee a specific unit. At least, that is the case with villas. Not sure if that is the case with houses, especially the higher end houses.

There are a lot of individual houses for rent on sites like VRBO - some may include resort amenities, and some of these may be the same as rent through the resort. You can at least get a flavor there...though it is getting late for this summer, especially as the # of 6+ bedroom houses on the rental market is pretty limited.

Note that the Kiawah resort gym is nothing to write home about. The pools, on the other hand, are great for kids, especially the one at Night Heron park. If you are looking for easy proximity to the beach, resort pools, park and fitness center, I'd look primarily at houses along Eugenia Ave. There are lots of houses further down the island, past the 2nd gate in Vanderhorst Plantation - and that is a more "exclusive area", and closer to the Ocean Course, but further away from other resort amenities.