The following advice is based on the assumption that you want to eventually acquire both adult level fluency and adult level proficiency in your second language. If you do not, then it's a whole other conversation. Having learned Japanese late in life, and also taught English as a second language professionally for 5 years, my advice is -- don't bother with grammar explanations. Instead of using Duolingo, read books.

There is nothing inherently wrong with learning grammar (and if you want to, I recommend reading grammar books in your target language). However, it is unnecessary. Memorising grammar rules will especially lead you down the road of approaching language like a recipe. The problem with grammar rules is that there are a lot of sentences that are grammatically correct from a prescriptive sense, but that are idiomatically impossible to understand.

Programs like Duolino are nice because the give you vocabulary in the context of sentences. However, you'll never get very much beyond basic sentence construction because you don't have the larger context. You don't know when to use one phrase and when to use another. You don't know the situations where idioms naturally pop up. You don't know how to organise your thoughts and to express them in the target language as opposed to translating your English ideas.

It's really funny, but when I read a Natsume Souseki book, I can't help but think how similar a writer he is to Dickens, and yet if I try to translate his writing to English it ends up incredibly dry and uninteresting. The charm of it is the expression in Japanese. Especially because Japanese and English are nothing alike, I find that I can't speak Japanese fluently unless I abandon English.

The thing that makes people worry is that they think that their second language is not good enough to become fluent. It's important to understand that fluency and proficiency are different things. Children are not at all proficient in their native languages -- especially 3 or 4 year olds are awful. But they are very fluent. With 2-3 years of Russian, you will also be awful, but there is no reason why you can't be very fluent with what you have -- and that includes reading.

It's too bad we can't have adopted parents in our second language to read us bed time stories because that would be awesome. But you can read by yourself. When I was very small, I had to be made to read because it was difficult for me. Eventually I got to the point where people had to tear the books away from me. The same thing was true in Japanese.

The advantage you have by doing it this way is that you have an endless supply of natural language. Your only task is to try to understand what it is saying. What I used to do when I was learning was to scan a piece of text to find vocabulary I didn't know. I would take about 20 pieces of vocabulary and look them up in a dictionary (I actually wrote software to make that efficient, because I'm a geek). Then I used a spaced repetition drill program (my own) to remember the vocabulary. Then I would read the text. Most of the time I could understand it based on vocabulary alone. If I ran into new grammar I would enter the sentence into the SRS drill with my understanding of the meaning. Rinse and repeat. Every week or so I would go back and reread bits of the book, updating my SRS data with my new understanding -- and it's incredible how quickly you form new understanding. After I read a section of text about 5-10 times, I could read it just like I was reading English.

After you get about half way through a novel, you start to learn the idioms that an author uses. You can then often read several books in a row without having to study -- just read them. But then when you switch to a different author, it's back to study mode. Of course I didn't start with novels. I started with picture books (Momotarou!!!), moved on to manga (great for conversational Japanese), then novels for elementary students and I'm currently in a phase where I'm enjoying books that are in the Japanese junior high school curriculum -- but at that point you're pretty functional in the language. I don't actually study at all any more (though I really should practice writing my kanji).

Not sure if any of this is helpful to the OP as well. I spent a lot of time writing my Japanese SRS tool (now sadly a victim of bitrot -- I don't think it even runs any more). I never could find a good way to really efficiently bootstrap native sources of information, but things like a built in dictionary and a deinflection/deconjugation tool are life savers. Honestly, if I were to concentrate on anything it would be that because Anki is already pretty hard to beat on any other front. Focusing on making it easy to create cards based on material found in the wild would be a great differentiator.

P.S. Last word on the grammar thing -- I actually learned Japanese grammar eventually. I had to teach English grammar in Japanese, so that forced me to read Japanese grammar books so that I knew what the vocabulary was. It was actually a lot easier than I thought it would be.