Oftentimes, "zij" is used to provide emphasis:
- Waar is Mieke? Ze doet de afwas. -- Where is Mieke? She is doing the dishes.
- Wie doet de afwas? Zij doet de afwas. -- Who is doing the dishes? She is doing the dishes.
They are generally interchangeable, however. When not emphasising, "zij" can provide a more formal feel than when using "ze". Most people would use the latter in this scenario, at least where I live.
No, you can check wiktionary for the IPA's (words written with the international phonetic alphabet). But be mindfull of the notation of g sounds. I ve seen errors. (Though many sources about /x/ and /ɣ/ contradict eachother as to what they would stand for. And some articles/sites talk about the difference between /x/ and /x/ while I see the same symbol twice! So far the rest have checked out so it is still a good place to check the IPA just disregard what it says for g's)
heardutchhere.net/DutchPronunciation.html#CH might help you with you pronounciation aswell. All sounds are explained.