Hi,
As you can probably tell from all answers, each person will find a way that better suits them to learn a new language. I think laguages like japanese (as in, with ideograms) do complicate things further, since learning grammar and vocab does not necessarily means learning how to read…
I am a relative beginner in kanji as well, but I did japanese classes for about one year in college and we were already studying some intermediate grammar points, which means that grammar is not something I have a lot of problems with. As long as I know the vocab and the kanji, I can comfortably understand the meaning of a sentence.
What this means is that, in my current point, focusing my time on kanji and vocab acquisition seems like a good idea, specially since it frustrates me a lot when I have to stop immersion time to consult dictionnaries. So ideally I would separate my study time into WaniKani, immersion through reading and texting with japanese speaking friends and vocab mining. In reality I do not have the time to do all of these so I just do whatever and try to keep up with my WK reviews since I feel like WK does pay off in the long term.
If you are just starting, it depends on how you want to tackle things, I do not think there is a necessarily correct way to do it. If you prefer to spend your first year mastering kanji, some vocab and not be able to actually use it, then just speed through WK and then tackle grammar, reading/immersion etc. This is probably not the most efficient way nor the fastest way to actually use the langugage, but it might be comfortable or less frustrating for you.
If you want to be able to read ASAP, then it’s probably better to focus solely on grammar through a textbook and just jump directly into reading, creating kanji and vocab flashcards as you go. I wouldn’t even use WK if this was my goal honestly.
Or maybe you can do a mix of both, just keep up with WK in a moderate pace and dip your feet into native material as you go. Search stuff up as they come and maybe do 1 to 2 hours of textbook lessons per week.
The most important thing I learned is that this is not a race. Pace yourself in a smart way and eventually you will arrive at your goal, even if it takes time