I’m doing this now-genki 1/2 and wanikani at the same time-but also I’ve done a lot of different types of “studying” Japanese so maybe a semi brief list of those will help you:
-first thing i tried was duolingo-it was great for learning hiragana and some VERY basic sentence structure but it sucked otherwise and I hardly retained anything. I did this for almost a year before trying to actually study using text books etc, sadly. I’ve also tried drops and lingodeer-two other apps- and while they are both better than duolingo, they’re still really limited. I haven’t found any apps so far that are worth using-but they can be ok for reviewing on the train or something.
-I started wanikani about 6 months after duolingo, and it helped me get into the habit of studying a little bit every day. Also, for me at least, knowing that I could read a lot more kanji than your typical in-classroom(hs/college) Japanese student was a big confidence booster. It still makes it 100x easier for me to learn and retain vocab.
I tried studying genki independently to no avail and switched to tae kim which worked pretty well for the first couple of chapters and then I really fell off because it got too boring to just read and read-maybe that’s not you and if so you’re lucky! I like tae kim’s structure personally, but I found out later in the game than i’d have liked that I really gotta be in that classroom setting to learn anything.
The first japanese classes I took were in small groups using the japanese for busy people textbook-it’s even more basic than genki honestly, but it has tons of exercises and i thought it was a good foundation. After that I was more or less able to skip through the first half of genki 1.
I finished up genki 1 in about 2 months, maybe 3? If you keep using it consistently and keep moving forward you’ll find that it’s obviously cumulative so I didn’t find it that hard to retain. As a tradeoff though, I’ve reaaallly slowed down on my lessons and vocab reviews so that I could apply the wanikani material i already know to the new stuff I was getting out of genki.
tl;dr : apps suck, tae kim is ok, super baby basic beginner: (especially if you’re studying on your own) Japanese for Busy People is pretty good but can oversimplify some things. Genki is solid but I had a tough time studying it on my own, and now that I’m in a class I find it hard to put equal hours into Genki and Wanikani. If anything, I’d recommend getting through your first 4-5 levels of wani kani and then start Genki, or study them on alternating days so you can avoid information fatigue. I do totally ignore the genki kanji cause it’s usually furigana’d but I’d think if you see it enough in the exercises you’ll eventually learn it, so maybe dont stress over that too much? These are obvs just my experiences and learning process, but maybe it’ll help you avoid some things that won’t work for you or find stuff that will!