All things are possible...with enough cash.
What you describe doesn't sound too difficult. Now if you want to move the kitchen or bathroom, that can get complicated as the plumbing often controls placement of features.
You may want to clarify what you mean by Class B. Some of the smaller ones are little more than a full size van but there are some larger ones that are essentially a Class C without the overhead bunk.
Obviously, if you really need to be able to park in tight spots, a smaller unit can be helpful but in most areas of the USA, parking is just not that critical. You may have to park a little further out but most lots can easily accomodate a decent size motorhome.
Once on the road, driving is no more diffcult pretty much regardless of size. You may want to take a few test drives to get a feel for it.