Yes, I was wondering about that worry as well. It is extremely unlikely to fail N1 only because you had problems with obscure kanji. It is good to have a look at them of course, but there are more fruitful ways to spend your preparation time. Even the people designing the tests would know it was just malicious to keep asking foreigners stuff you don’t need in daily life.
On the positive side after you reach level 60 (or rather say 30–40) it is easy to learn any missing ones (it’s not a shame to be a completionist). You already know all parts the kanji are constructed of, they are often semantic-phonetic compounds, and they are more regular in that regard. You won’t ask yourself the question “how do I learn the rest?” then, you can just do it.
I quite like Japanese for busy people as a resource for learning grammar and expand vocabulary/listening skills. Having tried Genki as well, I find Japanese for busy people much better for the self learner as it doesn’t assume you’re a teenager in a classroom environment. On top of that I’d suggest Lingodeer, a free app that also helps a lot.
Some unconventional aproach to learning grammar could be the one I do. I’m not sure if right away if you don’t have any background, but at least after the most basic of textbooks you should be ok to give it a try.
I do sentence mining using this method with Anki and some plugins.
I keep both the first 2 volumes of the Dicitonary of Japanese Grammar series and Handbook of Japanese Grammar Patterns at hand and resolve doubts as they appear in this terrific reference books.
Japanese the Manga Way serves as a great companion book for having actual samples with the use of those grammar points while explaning nuances in their use. I read it every week, it’s fun and a light reading, yet really clarifying in some aspects.
As far as grammar and learning it, I would limit all the SRS and nice apps to a minimum and just start reading (graded readers for japanese learners, basic japanese tales aimed at children, etc; and move forward as you see possible)
The SRS apps are great for memorizing… yet grammar it’s something your have to experience over and over to come through and get the actual uses for each grammar point.