I would advise to avoid areas hit by hurricanes, as fuel may be hard to come by or contaminated. You might consider running the 10 to the 20 into Atlanta, then 75 down to FL.
Also, use anti-gel and Diesel 911 every fill-up to help prevent fuel quality problems -- I've seen a bit of that lately with newly purchased buses on their maiden voyage home.
Moving at night into the morning and planning food / fuel / sleep stops during rush hours will be more low-speed friendly, fewer idiots and will work great if you can adapt to sleeping noon to about 8 pm.
Most hotels/motels have 11 am checkout / 1-3 pm check in, but some will allow early check-in, just make sure parking with easy ingress / egress is available nearby. People are stupid and tend to make things as difficult as possible for larger vehicles by parking too close.
As far as fuel, going by CK's 8 mpg (I got 7.5 running 70 with a Cummins 8.3 that turned out to be sick, rocking a 5-speed MD3060 and towing a car), the route I suggested is 2,750 miles.
2750 divided by 8 = 343.75 gallons, call it 345 just in case.
345 gallons times current natl average of $2.11/gallon = $725 for fuel. Call it $800 just in case.
Fuel really isn't what you should be worried about so much as blown tires, etc. It's good that you way overbudgeted for fuel, because you may need it if a tire blows or a brake hub sticks or something.
By the way, if you haven't seen my posts on the bus safety thread, should you blow a steer tire, do NOT brake. Floor the accelerator and steer against the pull until you regain control, then slowly back out of the accelerator until you can get it off the road safely. Braking at speed with a blown steer tire can cause the rim to dig into the pavement and possibly roll the bus.