Excellent suggestion: more Napoleonic sailors and marines.
If twleve more figures, say: two naval officers, two boat crew members, and four boarding/landing party sailors, and then a marine officer, sergeant, drummer, and-- _________?
That would make, counting the original set, sixteen sailors and eight marines, but maybe the ratio should be different for landing parties.
I do not think that 1/72 is a common sailing ship model building scale, but the ship model builders have a large range of ships' boats/fittings/cannons available to them.
I assume that a fair number of the Royal Navy/Marine figures could stand in for the early USN.
Barbary pirates also would be great--I know that there are some scattered figures in other sets that will work, but this would make for some interesting boat/landing party actions.
Howard Chapelle's "History to the American Sailing Navy" contains the plans of an extraordinary range of small gunboats and ships' boats from this period.