The track plan suggestions are all very interesting, but I strongly recommend you find out the minimum radius (that's the official measurement for 2-rail O scale) of the engine you prefer before you even begin building benchwork. You may find that your "curve corners" may need to be a little larger than 2' square to accommodate the curves that engine may need.
Anyone know if the AHM box for the IHB 0-8-0 indicates the minimum radius?
Chuck