I was mistaken - the adventurous is built on the chassis that has a 170 inch wheelbase - looking at the pictures I thought it was the older 140" short wheelbase. That should make my post less confusing. Sorry.
Handbasket's point about walking around in RV's is a good one. I note that the Serenity has the 54" corner bed that is common in Sprinter based C's. Try that out. We would feel very crowded in that bed and we are not large people. Go to RV shows and check things out - imagine doing your normal things with the floorplans that are available.
There are a number of other small C's based on the Sprinter chassis. They all have different layouts and you should look at them. Class B's are also made by a number of different companies and you should check out other brands besides Roadtrek.
We chose to get a Sportsmobile converted Sprinter van in large part because we were able to design our own floor plan and had Sportsmobile custom make it. This is a worthwhile approach for B's because the space is limited and you need to make it work for you. The price will also be much less.
Here are a couple of questions for you:
Will you spend lots of nondriving time inside the van or will you be out doing things most of the time?
Where do you intend to go? An 97" wide vehicle is fine on freeways and major roads but is not so wonderful on secondary roads and is a bear on anything worse. Lots of suboptimum roads lead to interesting places.
For us the versatility and easy driving of a B van trumps the extra space of a class C but sometimes we are envious of those with more room.
Advanced RV Sprinter