When the number of men per officer Samurai exceeds 20, excess men retreat to the rear. Ninja are used mainly to raid or ambush. They are of limited special use on the conventional Japanese battlefield, but since so many people like them, we added them to the rules. Ninja can act alone or in small groups. They do not need an officer.
Musketeers usually fire as units, and are brigaded next to spearmen.
After firing, musketeers reload while spearmen fend off any attackers. Like the fictional Fanrengi space profiteer, Quark, the daimyo's main goal is Acquisition. He wants lands and goods and power to enrich his little fiefdom. Each side has a certain amount of bales stashed in their territory - say one per house, ten per castle, etc. The goal is to carry off as much as you can.