Try to relate it with the English doe /female deer/. Both of these words come from an ancient word that meant "to suckle", from which also comes the Latin femina. The later, though, evolved differently so it doesn't sound similar to dziewczynka (pIE *dh > pIt *þ > Cl Lat f) and is not of much help for memorization.
- polish language has 7 cases, that means every noun has potentially 14 versions 7 singular and 7 plural.
Some nouns have different cases look the same, some have those cases identical by definition, some by exception, some by something in between.
Dziewczynki, like almost all feminine nouns in plural have nominative=accusative=vocative
Not really. I mean, you can listen to this word on Duolingo.
In Spanish you don't always have the "dzi" sound. You, might depending on your accent, pronounce your "y" as Polish "dzi".
Polish "y" is distinct from Polish "e". It's always pronounced the same way, like in English "rhYthm".