I’ll definitley agree with @EiriMatsu that you can work your way through some easier manga like Yotsubato quite early. It always depends on how much you’re willing to look up though.
I also learned english mostly through reading fantasy novels, but that was because I already knew some vocab and english grammar came more naturally to me.
To me (Being WaniKani Level 10 and having worked my way through Genki 1, which is ~N5 level) reading is still too much of a bother.
At the end of the WaniKani Guide there’s a section called “Using My WaniKani Knowledge” that gives a nice perspective of what you should be able to do.
Completing Tae Kims supposedly get’s you around JLPT Level N4 (?) which, combined with the right WaniKani Level, should be enough to work yourself through easier materials.
Then again, havent been there. So I’m just guessing 
Also, just gonna leave this here in case you didnt come across it yet, because I think it’s great for learning through reading: