Carrying capacity of Illinois farmland is already sky-high, so planting a food plot in that kind of situation is not really affecting that so much. You stated that you mainly see deer on the 'ends' of your property...look at what they have ready access to on both the east and west sides...cover. I'd plan on increasing cover, especially in the center of your property, to have a better hunting property in the long run. Food plots are a great attractant, but they are also a money pit. I'd try to minimize the total acres of plots you put in annually to no more than 3-4 acres...and limit those to ~1/2 acre 'hunting plots' in strategic locations next to cover and areas where you can have stand locations where you may hunt on any given day no matter what the wind direction.

As far as stand locations go...inside corners, 'fingers' that jut out into the fields and intersections of the corridors that I have pointed out are all excellent locations...as well as along the creek. I'd place a stand just inside the treeline east of the corner of where the sumac/brush area and the winter greens field meet...which would be just slightly north of the creek. You should have a shot at anything going down the creek as well as anything using the sumac or greens fields.