how much for a walnut edge grain for a 4 foot by 4 foot island-- we would like to have our two kids to be able to sit at it so would we need a 12" or 18 " overhang?? Also the width would need to be slightly wider --since we wouldn't want it exactly the size of the cabinets. Do you round the edges?? Would hate to run in to a pointed side. Thickness around 2"- 2.5" and our zip is 60102. Thanks!!