I would get a geotech engineer involved to make sure your rock does not have fractures that would make keeping a lake full of water difficult. Also, if you rotate the course about 5 or 10 degrees, it will make for an easier set up for the driver and skier and help to prevent bow rollers when turning in to line up. I did that on my lake since I did not have room to offset my islands. You will be surprised what a difference a few degrees makes. I have one buoy only 45 feet from shore and its really not an issue. If you decide on an island, keep the top of the island no more than 18" above the lake level. My islands are much higher and the muskrats have caused a great deal of damage. If you keep the top of the island low they will not have room to get a den above the water level. Most of my lake maintenance is on my islands......muskrats, erosion and mowing.....never ending.