Oil pressure. That is about all I need. Tach is nice when first setting the boat up and getting the feel. We run oil temp too. Idiot light on oil pressure in case you are racing. Water pressure is a nice idea, but an idiot light on pressure will always be on unless you are going 20mph. If your pickup gets plugged, it will tell you. Temp sometimes won't, as we have had no water in the block and that doesn't tell you the temp of air real well.