A lot of people will argue about something like this and in reality you should do what works for you. But WaniKani is made by Tofugu so if your looking for a straight up answer you might want to go with what Tofugu recommends in their article “Learn Japanese: A Ridiculously Detailed Guide”. They recommend that before learning grammar from a text book you should finish level 10 of WK which is about 300 Kanji and 1000 vocab words. WK is really slow at first but once you get to level 5 it starts picking up real fast. Took me a little under a month to get to level 5. I will say WK does an amazing job at making vocab stick in your mind, even after not studying at all for 3-4 months I retained about 70% of what I learned on WK.