Cost of insurance is a hard number to advise you on as it varies by states, cost of unit, miles driven, and so much more. However, I pay a bit over $400 a year for my 14 year old 31ft Class A through Progressive.
As far as MPG, not sure you will see a lot of difference in a V10, 460, or 454. Set you expectations in the 8-9 mpg range over several trips and tanks. How you drive, where you drive, what gas you put in it will have a bearing. You might get as high as 10 sometimes, low as 7.
2016 Newmar Bay Star Sport 3004