My Early Modern Eastern Europe wargaming mostly follows the game By Fire And Sword, since I figure they have access to non-English-language sources. At risk of oversimplifying, they divide the Zaporozhian infantry roughly as follows:
Registered Cossacks - elite irregular musketeers
Moloitsy - standard irregular musketeers, with option to mix in a proportion of spearmen
Plastuny - ranged skirmishers with rifled firearms, representing scouts and pickets
Swashbucklers - melee skirmishers, representing specialists in Black Sea piracy and river raiding
And as WFGamers says, they relied heavily on cover (terrain features, settlements, wagons, or field fortifications if time allowed), or mobility via boats.