You certainly have focused on two of my “must haves” and they being tank size and storage space (both inside and out) especially if you plan to boondock or stay at campgrounds that are not full hook up. In answer to the levelers, after owning several motorhomes, I will never consider one without levelers. The fully automatics can be nice, but ones you do manually (push buttons) work well to.
I have looked at the Mercedes and have heard good things about them. Keep in mind they do get mush better fuel mileage, but maintenance costs and fuel costs are typically more than a gasser.
Before you commit to a C, take a look at some smaller class A’s. Newmar makes some very nice short Class A in the 27-29 foot range, with good storage, and because of their size are easy to maneuver.