Welcome to the Newmar forum & irv2 dustytwo.
Congrats on your new Newmar and congrats on your first safe trip.
Have been in that part of country sure different than east coast just great country.
Your water tank should have a stamping on it by tank mfg that should give the gal size. I have two tanks either side of main rails tied together with a 11/4" pipe.
Fuel gage will go about 200 miles on full before starting to drop down and about 10 gallons left at red mark.
Mileage is pretty good, did the coach have the
Brazels UP upgrade installed before you got it?
Enjoy the forum and do post often.