My F450 is a 2010, but it is a Lariat. I'm not sure what removable tailgate means, but my tailgate with step is very heavy compared to one with out. If I remember right it weighs about 100 lbs compared to a nonstop that is about 60 lbs. It also has a camera builtin. It's fairly hard to remove/install due to the weight, but still removable. It would be hard for me to believe that the Ford will build a tailgate that can't be removed, but who knows. I'd ask the dealer about that feature.
As far as F450 pickup vs F550 chassis goes, we wanted a truck that looked more conventional at the time without a flatbed. The spring pack and frame are quite a lot different between the chassis cab and pickup with the chassis cabs having a straight frame. All of the chassis cabs have more capacity the last time I looked. You may find that even the F350 Chassis has as much capacity as a F450 pickup.
We have a 9 1/2 ft heavy camper. If you go larger, maybe you really need a F450 chassis or F550 chassis.