Marching figures are the best for me and I could handle just a box of them. Don't care if they are all identical. However, it really depends on the subject. For example, British line infantry would require a large number of marching figures, whilst Portuguese Cacadores would need a good variety of action figures.
As I need large numbers of figures I don't mind them all marching. It does look a little silly as a column of infantry moves down a lane all in the firing position!
Marching was the most common activity for soldiers of the period. So I can't really answer the question other than 8 or 12 marching figures for most units (basic line infantry)and 2 marching, 4 firing/loading 2 advancing for special units (cacadores, rifles sharpshooters, etc).