Fresh water is just fine. Remember there are motors out there there in the briny all year round. You can run the engine then disconnect the fuel supply to drain the carbs. Not sure what the approach is on 4-strokes? Some folk state-side suggest Salt-Away or white vinegar. however it seems a little unnecessary.
One thing that's worth checking is the thermostat. You will need a new gasket if you investigate, but it's worthwhile to lightly brush it with a brass wire brush. Steel brush is a little rough. Also check the thermostat housing for salt build up.
Regards greases and spray oils, I'd avoid Duck Oil. Try WD White Lithium Grease or Quicksilver Corrosion Guard on linkages, etc.
Is that with or without VAT?