We had a Sunnybrook fiver and then I decided to go Class A. It was a 40 footer dp. After several thousand miles the Class A did not suit our travel style especially after looking at the upper end of new fivers. New fivers have auto leveling systems, and honestly there is very little difference in setting up the newer fivers vs a Class A speaking from experience.
The advice on getting a truck first is definitely the way to start. I sold my F-250 and went with a F-350 dually so I could get the floorplan and the fiver we wanted. Diesel is something you will not be sorry you have. If fuel mileage and the cost of oil changes cause heartburn you probably need to rethink the rv lifestyle in general.
Do as much truck as you can first and then start your hunt for the perfect fiver for your family.