before you dive in, there are a few things to note. from looking at your photos and reading your ideas, putting walls up in some areas just seems like they wouldn't make sense or fit in that area.
pic 2 and 3: i could see removing the banister and putting up walls...and then opening a doorway to the living room. However, I would make this a wider (double sized) archway instead of a standard doorway. living room-kitchen transitions are typically high-traffic areas and I personally HATE having only 1 entrance/exit in the kitchen -- especially when entertaining. You could add pocket doors or french doors if you really wanted full separation.
pic 4: is this the living room/dining combo? I would simply set up zones in this room. you have very little furniture here, and once you fill the space appropriately, it will feel separated
I agree with PP about trial running some screens, or hanging curtains as walls for a couple weeks, or finding tall bookshelves to put up (added storage - yay!)
...as far as resale, the trend IS towards more open floorplans. so this may hurt your resale. that being said, people love houses of all kinds. so who knows.
hubby and i have a fairly contemporary open layout as well. the only room that was completely closed off was the kitchen -- so we knocked down the wall and created a half-wall between the rooms that is our bar/kitchen island. it's truly awesome and i love being able to watch hockey/football games/movies while i cook =) our kitchen used to fit 3 people, and now we've had 10 in there without worrying about bumping into everyone!
to design things, i used a computer program (ok, i used The Sims) to 'build' the house, and arrange furniture and see what the renovation would do to the space. it was an awesome idea, and i loved having a 3d view before we went ahead and did it. maybe try something like that too?