How many nouns? Do you mean how many genders?
Well, in singular you have masculine, feminine and neuter. There is one case (Accusative), where it is also important whether a masculine noun is 'animate' or 'inanimate'.
In plural you have 'masculine personal' plural (almost only 'groups including at least one man') and 'not masculine-personal' plural (as the name says... basically anything else. dogs, boxes, women, houses, everything without men).
Yes, "kaczor". "Donald Duck" = "Kaczor Donald".
But we generally don't accept other words for animals than the 'default species name'. It may rather create confusion when suggested to the learner, than be helpful. And frankly I don't think you'd hear "kaczor" often outside of conversations about the citizens of Duckburg (Polish: "Kaczogród", if anyone's interested).
Are you really asking about 'eating duck' (je kaczkę) or did you mean 'bread' and focused on the difference between "eats" and "is eating"?
In general, "eats" and "is eating" can easily be translated the same way, into "je".
But there is also a so-called 'habitual' verb for "to eat", and that is "jadać", so here: "jada". This works only for Present Simple. It's not taught in this course, but you can encounter it, it's not something rare. But the plain "jeść" can easily be enough.