I will grease the impellers with Motul Tech Grease 300 (Multipurpose grease, formulated with synthetic base oil stocks and from complex lithium soap, with extreme-pressure, anti-wear, anti-oxidation and anti-corrosion additivation).

My 2012 add about 435h when I bought it and now 500h (I did 65h this season). In the indmar manual they say to change spark plug annualy, that's why I plan to do it.

I'm not sure to understand your last point... I don't plan to fire the boat up at the ramp but at home, do you mean I should connect the fake a lake on the ramp first and not at home ? I never plan to fire up the boat without the fake-a-lake. In wich case ?
Thanks