I'm by no means an expert...we only stayed in the cabins once, last February (but we had such a great time, we're going back in December!) I'll just share our experience. We stayed in Loop 2600, and we loved it...right across from the smaller pool. I've heard 2500 and 2700 are nice, too. Maybe some others have good points about the other loops.
About the golf carts...it really is a personal decision. I brought five kids, and two of them were 5 and 7. Our cabin was pretty close to the bus stop. We were there at a quieter time, and we thought the buses were great, and we relied on them solely for our transportation. We didn't rent a car. Money was an issue, so we did not rent a golf cart. I think they look like fun, and would be very helpful with anyone with mobility issues, but I wouldn't say they were necessary for your average family. Fun...yes, necessary...no. Just my .02 cents....
I think you'll have a great time!
P.S. Are you going right over the Christmas break, or earlier in the month? I know the more crowded times will make everything busier, including the buses. But I think it will be okay if you just realize that, and plan accordingly.