If at some point you want to re-place the brown leather chairs this style of chair with rattan sides looks perfect with beach casual style. You don't always need a pair. The brown chairs could be stored and used in another house at some point. They are great chairs -just not for this room.

Egg crate bookcase from Plummers.





With this floor plan you would move TV to the wall opposite the sofa. That would leave the back wall empty. A wall unit would be placed on that wall for books, cd's movies, etc. Another idea would be to look for an old antique table on that wall. If you found one at least 5-6 feet long (not too deep) in an old wood with a beautiful patina you would still have room for the tree in the corner and an extra arm chair. Asian prayer tables also look wonderful in casual beach style rooms.You could hang art work over the table and place a lamp on top. A room this size with high ceilings eats a lot of light at night so you need many light sources in the room.