I did the Disney/US thing in Feb as well, and if you're planning on staying on Disney property, you'll most likely want to rent a car for the few days you're going to US. You can always take a shuttle, but you'll be at the mercy of shuttle times and for the price of a cab, you could have a rental for that day and the freedom to come and go as you please.
I stayed at ASMu for the first three days, then moved over to the Sheraton for my two days at US/IOA. I had a rental the entire time and, in retrospect, I probably would have been better off staying on Disney property and driving to US both days. I found myself opening the parks and pooping out around 4:00 or 5:00. If I had been on Disney property, I would have come back to the resort in the early afternoon after US, taken a rest and gone to Epcot or DS because they're open later than US would have been. Besides, Disney magic is sooo much better than watching TV or swimming in the Sheraton pool!
But that's just my opinion. I went alone and don't know if you kids or others to consider.