For a class C of the size you're looking at, somewhere around 7.5 to 8 mpg, give or take, would be a reasonable estimate. As others have said, it will depend on your speed when traveling to a large extent.
A class A of a similar size will get similar gas mileage, maybe a hair worse (and maybe not), and will be more maneuverable. The turning radius of large class C's is about as bad as any vehicle on the road, and there's a good bit of tail swing. It is not undrivable or unusable by any means (I have one), but they are not maneuverable vehicles in comparison to...well, most anything.
Setup and tear down time is largely dependent on how much you decide to set up and tear down. Even with manual leveling (via ramps or blocks), the leveling and parking is a job of a few minutes at most. It's the things like moving stuff around the inside, setting up the chairs and awning and grill and signposts, hooking up the water and sewer and electricity and cable TV, etc. that take a long time. (Not having a slide will also speed up setup and tear down, for that matter.)