Don't let the case endings scare you - many people from the ex-republics, especially the Caucasus, hardly ever get their case endings and genders right - we don't mind. I think vocabulary is more important. You'll learn case endings and gender with time, and even if you never get them right in most cases, people will still understand you as they understand the non-native speakers from the ex-republics. It would be nice if a foreigner used his/her cases correctly, but I imagine it can be easy for some students to get bogged down in them and never get along with other grammar and vocabulary, so don't dwell on them for too long, rather move on to do other stuff but do come back to them again later on in your studies when you have learnt some more vocab, some fixed phrases, etc.