I started working through imabi while having very limited kanji knowledge, and just wrote down the supplied furigana for kanji I didn’t know from the early lessons and gradually began writing down kanji as I learned it. In the beginning there was almost none:
Whereas now it’s nearly all kanji:
There are so many benefits for this. For starters I don’t have to do a huge amount of grammar catchup now. I’ve learned lots of words using kanji I know from here but with vocab that is not taught here that I’ve added to my own personal anki deck. Also, the motivation boost I get when I review grammar material and physically see how far I’ve come from chapter to chapter is very rewarding.
When you’re doing grammar with vocabulary you dont know, as long as you know which Japanese word corresponds to which English word in the example so that you understand how the grammar works, that’s all you need. Looking up every word as you go is a waste if time. Just have that focus for what part of Japanese you’re studying, and over time it will all slowly fall together. Reading the vocab example sentences in the same way (skipping over words or grammar you don’t understand) will have the same effect; you will gradually notice that you just get it; a lot more frequently.