cook1, I can't answer the question about exactly how the 30" is calculated vis a vis the overhang because I haven't seen mine yet but my impression is that it is measured the same way a 24" cabinet is..ie., exactly 6" deeper than a 24". But, yes, you can put a 30" cabinet on just one side of a U because we are doing it. Now, our U has a break in it at a door and at that point there is a transition space with a pantry and fridge before we pick up again with the 24"...if it were continuous, I'm not sure how you would make the transition. I hope that helps a little.