Update on #LearningDanish: I have completed 3 of 45 units on Duolingo and 1 of 4 units on Mango Languages. I think I'll run out of content rather quickly; there's not as much as, say, the French course on Duolingo (which has more than 200 units). I'm starting to wonder what could fill the intermediate space between materials for beginners and native speakers, though I still have some time to think about it.
Most of the lessons have been about indefinite, definite, and plural nouns. This seems straightforward, though I do struggle to pick between endings like -erne or -ene; I suppose that comes with practice.