my suggestion is to do lessons with a case per lesson explained and praticed and every 4 lessons a contrastive lessons eg the difference in use between LOCATIVE (in a lesson on place and movement) and ACCUSATIVE. And a lesson on time expression WITH DATES because that's tricky with different cases . pex a day where someone goes from one place to another and then tells about it to someone else" i went to ..., I went running in the park, at school I ..., "
a few lessons on perfective imperfective because that's hard too for any learner, regardless their native language.
I look forward to a series like the newbie series of japanese pod 101 and intermediate lessons should include past tenses (imperfective), conditional tense, comparison, difficult plurals.
* As for advanced something on Poland's history would be nice and interesting. I think the audio blog is excellent!
* Reading ( fragments of) poems or fairytales also seems a good idea to me eg snowwhite, alice in wonderland
