My boat has one large 500 gallon tank....each engine has a pair of Racor 900's with vacuum gauges, and my genset has a pair of Racor 500's so I can change over if needed in a hurry.
I would think that if you were to put a pair of 900's for each engine, and a pair of 500's for each genset....you will have plenty of filtration and water separation.....
Psst....if you use Racor's....get the stuff from "Hopcar"...... He has good prices on them.... Racor Fuel Filter Water Seperators -Marine Turbine Series
Filter element prices are really good too.... Its where I get mine!