Making a Japanese Quick Guide, might need help

Hello, I’ve been on this subreddit for sometime, but only just lurking or replying to some posts.
I’ve been learning Japanese sporadically over the past 5 years. I recently finished an intermediate course and a culture course and am now self-teaching to prevent losing what I’ve learned.
I thought one way that could help is to make a short, but informative Japanese quick guide that contains information on grammar points, kana, and conjugation. I might do some kanji, but I feel like that might need it’s own separate notebook or something. I wanted to make one not just to help myself but also my sister since she’s expressed interest in learning Japanese for fun.
Has anyone done something like this before? How did it turn out and what advice or examples can you give me? How much information should be in this guide?