As someone who followed the same method (DuoLingo for vocab, start reading, start talking) and now speaks a second language fluently, I'm not OP but I'll go ahead and vouch for their comment.
Completed the tree, but admittedly it was shorter back then.
I also did it in parallel with the Language Transfer podcast, which I've mentioned on HN before but is an amazing resource for understanding how a new language works structurally and grammatically.
I did find Duolingo valuable, but purely for vocab.