I run John Deere guidance. I would go with something that alows auto steering. We first started with a light bar they work ok, but sometimes you get to watching the light bar to much instead of whats going on behind you. Also you mentioned spraying. Using an auto steer system you will use so much less product it will blow your mind how much extra you have been using. Skips and overlaps not only hurt productivity spraying, its not good for whatever crop or grass your spraying. The last point and most important I believe auto steer will put you in a lot better mood at the end of the day. You can watch everything around you and not worry about following a foam mark with the skips and overlaps. I am not to old and was very proud of how straight I could plant following a mark, so I drug my feet about getting it, but after one day of auto steer I havn't even thought about going back to a marker.