Shopping for Class B Diesel. Advice for newbies please!

NCWriter, thanks so much for the basic info. Thats the kind of stuff I wanted to know. Your knowledge and wisdom is much appreciated. Thanks to everyone responding. This is an amazing wealth of knowledge. Many questions I have been pondering are answered.
One more question, I had assumed the Mercedes diesel engines are all the same, except for modifications as they get newer. Is that wrong, and if so which is better?