If you are driving, bringing bikes is the way to go. You can take bikes so many places at FW, some places even the golf carts can't go. Plus, the golf carts, even from off property rentals, can get very expensive. If you are patient - a golf cart is not a necessity - fun, yes - convenient, yes - but not necessary.
I have stayed at FW and never rented a golf cart. I do bring a bike. I do not find the internal transportation to be bad at all - you can stay in the cabins without a car and get by using Disney transportation. But as a previous poster said, it is convenient to drive to all the parks except MK. The best part is not having to circle the parking lot at the end of the day searching for a parking space.
The cabins themselves are very nice. Four people should be accommodated very well. The bedroom has a full size bed and bunk beds, and the living room has a double Murphy bed. It's nice to have two separate sleeping areas. It's nice to have the full kitchen even if you don't intend to cook full meals. Having the full size fridge is great for keeping plenty of beverages cold, and the microwave is great for easy breakfasts and snacks. There is a dvd player in the living room, so you can bring one or two of your favorites along if you like. There is only one bathroom, but it is a little larger than your average hotel bathroom, and it's refreshing to have a bathroom window! The bedroom is a little on the small side, but it does have a TV and vanity area. It can help with the bathroom schedule by giving another place for someone to finish getting ready to go out and about.