Before our first trip, I thought 12-14 mpg was doable. Ha! Was I wrong. but mileage is speed and terrain sensitive, so if you can stand to drive 55 mph on the prairie, you'll probably get near 12-13 mpg. The hair on my neck stands up when 18 wheelers bear down on me at 75.
We spent 7 wonderful years in Sacramento and we miss California, but, as a retiree, I can't justify the cost of living out there. You'll really notice the difference in humidity as you travel east. We would frequently awaken to condensation running down the inside of the windows, but the worse thing was a small leak in the slide out and the effects of condensation on the drawers under the dinette. Instant mold! That's when we started with the Dri-Rite. If you have that setup in your FF (It's the 189FDS model), after the trip, take out the drawers, and check the carpet inside the dinette base and under the table. The wet carpet is a great mold breeder.
I still have the factory showerhead because we don't use it much. It's like wrapping yourself in a shower curtin then trying to hit various body parts with a squirt gun. Anyway, to turn on the shower, first turn on the water in the sink, adjust the temperature, pull up on the knob above the faucet, wrap yourself in the shower curtain, and press the button on the handheld shower head. It'll be an adventure. By the way, do you know how to turn on the electric option for the DSI water heater?
You sound like my wife and I. We do okay until the third rainy day in a row then cabin fever sets in and I'll drive a hundred miles just to watch her shop.