Hi JawaOwl!
Welcome to WaniKani. If you’re having fun learning kanji with WK, don’t stop. There are free grammar resources out there too.
Have a look at this thread which talks about self-study and textbooks: What's the best textbook for self-study?
I think I posted in there and mentioned Nihongonomori’s YouTube channel. If not, I recommend that (to supplement a text book or an online resource you read).
You also want to look at this list of FREE stuff: “What Do I Do Now?” thread