At the beginning of the sentence - why does duzi end in an 'i' and not an 'e'. I thought the neutral form of the adjective is used with plural nouns as 'małe zwierzęta'.
Yes. In plural, there's the masculine option which works for male human groups and mixed human groups, and the feminine option which looks like singular neuter and works for everything else.
I don't recall many. (both żi or rzi) there is żigolak (which is from french gigolo) and I think all rzi are pronounced r-zi
in Russian it's the opposite: you can't write жы (ży), you always have to write жи (żi)