We did the exact same thing. Stayed off-site, and ended up with a 2-bedroom condo. I did extensive research and happy to share with you.
First, there's the on-site vs. off-site debate. I'll let you draw your own conclusions but there was no comparison for us. Making our own meals and grocery shopping was a heck of a lot cheaper. It made our vacation possible.
Second, there's the car-rental question: We did rent a car and that made staying off-site worthwhile. We were 10 minutes away from the resort and could come and go as we pleased. Zipping to
Walmart for a quart of milk was super easy.
As for the accommodation: A lot of people say to use priceline. I don't get this. You have no idea what hotel your going to get or the amenities your hotel will have. As an alternate, we ended up using Hotwire which shows you the amenities. It was important that we got a hotel with a pool (most do), but we were also able to get other amenities we wanted like: 2 bedrooms, 2 bathrooms, full kitchen, free parking, free wifi. We ended up getting the LBV Resort or something like that for something crazy like $90 per night. LOVE IT.
This is a good resource to help you if you're considering the Hotwire route:
www.hoteldealsrevealed.com. It will show you what hotel you're likely to get. We used it for our trip and got LVB Resort.
I looked into other alternatives like VRBO and AirBnB. In the end, we found what we wanted on HW. Pound for pound, I would rather rent from a hotel just because of my personal biases toward a renting hotels over somebody's house.