About the comprehensible input theory I have been using this method consistently for almost a year now to teach myself Russian.
It really really works. Initially I focused on learning grammar etc through online course etc but it didn't work for me. When I started focusing on consuming increasingly harder input in Russian (news articles, tweets, short stories etc) I saw a huuuge difference! Your grow your vocab tremendously fast and grammar rules are acquired naturally. I'm not saying it's easy I just say that that method really worked for me.
I tried LingQ to help me and even though is a very good resource the UX is incredibly bad and the free version is even more limiting. To the point that I decided to create my own tool talkabl.com. I decided to open it for free for any language learner.
It's an ongoing experiment on how much of the language learning can be automated :)