As others have said, I’d definitely recommend Genki I and Genki II for grammar (they’re only around $50 each, which is pretty good for a textbook), since they’ll give you all the fundamental grammar for Japanese. These two books teach everything from です (to be)/じゃない (not), to なきゃ (need to (casual))/なくちゃ (feel obliged to), to しまう (when something regretfully happens), なら (if; under the condition that…), 上げる (give to others) vs. くれる (receive) vs. もら う (get), 欲しい (want (a noun)), and て forms, which are probably one of the most important and fundamental grammatical concepts you’ll ever learn (seriously, you can do so much with them). Right now I’m around a 1/4 of the way through Genki II. The two books also come with CD’s for listening practice (which I don’t use a ton, tbh).
I should also point out that even if you do wind up using WaniKani, you should still learn the kanji in the back of the book. The two books together teach 317 kanji (145 in G. I and 172 in G. II). It teaches them as it pertains to your vocab.
Tae Kim’s Grammar Guide (he also has a website, as you probably already know) is more reference material than anything, since concepts aren’t thoroughly explained and there aren’t any exercises to reinforce grammar (and vocabulary seems kind of like an after thought). That being said, the points are still explained very concisely, and sometimes I’ll read a passage if I’m a bit muddy on something. I gave a quick look at the slang section, and already know that じゃない can be like ね, in that it seeks confirmation from the listener (exactly like “isn’t it?”). For memorizing vocabulary, I usually use Memrise (more specifically the Genki I + II courses).
Although I personally haven’t used it, the go to book after Genki II is Tobira.This book will teach you upper-intermediate grammar and 503 kanji.
Good luck on your journey to learn Japanese! It’s a long, bumpy road, but I’d say that learning Hiragana and Katakana is more than most people ever learn with the language, so that should be an achievement on its own. I wish you the best!