Yes, ü sounds like the ü in über and ö like Österreich at least. I'm not entirely sure about the German vs Estonian pronunciation of ä. Sounds closer to the ä in Käfer than the ä in Käse if you go to wiktionary and listen to the example pronunciations. I did study German in school because it sounded preferable to learning an entire new alphabet and recall the German ä was taught as sort of a cross between the Estonian ä and Estonian e, leaning towards one or the other depending on context, but then again I'm not sure how good my German teachers were, I know I only ever had two or three English teachers out of like 8 or 9 that actually spoke the language and knew how to pronounce words.