This post would be better suited under design dilemma section.

It definitely seems possible to add the extension you're talking about, but I'd post the discussion to a more suited topic. Also include any sketches or plans if you have any.

Before you get too far into the thought process, I recommend that you visit your local building department to find out what will be permitted. They will be able to tell you how much additional square footage you're permitted to add to the house or if you're already maxed out for the size of you property. Once you have that information you can then plan realistically, knowing any regulatory limitations.