Considering the amount of driving/touring that you want to do and the fact that you want to spend your daytimes outside the RV, choosing a B would seem like a no-brainer.
The problem you have is that you want features that are going to be hard to find in a B and I think you are going to have to make some compromises.
We have similar interests and are quite happy with our Sprinter-based class B but we get around the tankage problem by mostly using the campground facilities. This is a pretty viable option unless you have problems with using the same facilities that others use.
If you choose to go with a B I would second Davydd's suggestion of checking out custom builders. Our conversion van was assembled by Sportsmobile to our exact specifications and they did an excellent job. Check out their website (www.sportsmobile.com) for a lot of info and look at their sections on designing your own B.
Also, I strongly suggest renting some different type RV's before you make a final decision. What looks good in theory might prove unworkable for you in practice.