#1 Fresh water. Use Magnesium anodes only.
#2 The cylinder end caps can be drilled and tapped for the anodes. Ive done many. Sierra 18-6089
#3 I have also added the horseshoe around the front of the drive. Also Magnesium. Sierra 18-6240
#4 The anode plate above the prop. Merc #76214A6 Magnesium.
If you need a wiring diagram for the Mercathode, let us know.