In my honest opinion the intensive cases course should be mandatory for anyone studying Russian. I have been to school, had private lessons and never ever have I seen a course, that was able to make cases so easy. Tips, tricks, exercises and if you want a chat group to help you when things get rough.
Give up on spending useless hours on the internet looking for explanations. Stop looking at those horrible charts that make no sense at all.
Do yourself a huge favour and take this chance.