Whether gas or diesel, I would take a look at the 3500 SRW models too. If you get a diesel your "door sticker " payload for tongue or pin weight will be less cause the engine is heavier if that concerns you. Technically I dont think there is a lot of difference other than a little suspension and its mostly a "keep it at 10000 gvwr" regulation thing, but others will chime in I am sure. I ended up going gas and staying in a 2500 bit I saw some F250's with the diesel that barely exceeded the payload numbers on my former half ton. If I had gone diesel it would have been a 3500 I think just to not worry about it and enjoy camping.
The price difference is non existent to negligable from what I found, although check into your states registration for cost differences there. I actually saw a few cheaper at year end sales time, but they werent local.
I think that length will tow fine, but you will start to face some campgrounds that wont work as others said. My 35' is hard at some county or stare parks with lots of trees to maneuver sometimes. Newer campgrounds and pull thrus should be fine however