I have 2 V10s and in 2wd form without a lot of crap on the roof (racks, lights, etc.) they get about 10-11 in mixed hilly and flat country. I just converted one to 4x4 and put 34" rubber on it and it went down to 9.5
V10 maintenance is nil, probably less than the v8. They are an extremely durable engine and don't work nearly as hard in vans as the v8's do. The only thing I've ever done to a v10 is put new COP's (coil-on-plugs) on one of mine.
CarringB is an excellent source of info on the V10. He abuses the piss out of his and has around 400k or something on the drivetrain. PM him if he doesn't see this and respond.