Step ups are not uncommon for rear bedrooms--they may also provide for more storage underneath.
I have to admit I also like the bunk area. I have seen units that will allow you to use the space as a desk when not being used as a bunk--that would be great for full timing.
As far as the weight issue, all Class C's are more limited in carrying capacity. They use the same 450 for everything from 24' to 32'. Draw your own conclusions.
Why are you looking at Class C instead of A? Do you like the idea of having a truck cab?