right! Why wouldn't they put more important or common words in this section of lessons.
Because now we are learning reading and these words are pronounced just like in english but wirh different accent and letters
No, 즈 is a tranliteration for the /z/ sound in English (which is often how the plural "s" is pronounced).
The actual Korean plural marker is 들 as in 남자들 (Men) or 책들 (Books)
No, ㅈ is translated to z ,so when there's written something with ㅈ it means you have to spell it like a z (sorry for bad English)
This is random but I'm listening to BTS while working on Duolingo (sorry not sorry)