Andrew. I like your ideas, and floating shelves are cool. But, like most of Henry's posts, I agree about "loading". I have designed and built untold counter tops, and they all have been a "stage" at some time or another. Let's just say, "if you build it, they will jump on it".
Let's compromise. You are doing "country, and that lets you do all kinds of things that "approach" floating. Actually, when I think of floating, I think more contemporary. So, how about a nice historic, doric, bead board, whatever, column that holds up one end of your counter (or both ends) as and example? Support the other end with the same or cabinets. Eight feet is a lot of span no matter what you are doing. Then, you actually "accent" your country look with "details" that are country. You will seat all you need to sit, and you will be happy, "and" your counter top will survive.
If your "country" is rustic, I just saw cool "twig" designs on HGTV that you could do with stumps of trees..........see, let it looss, man.
If you head this direction, you can put in "any" surface ya'll want.
Think about it, look at mags, or hire me. I am cheap.......(forget this last comment, I do this this board for humanity...........)