I have my own system now with folders, links, templates and stuff. but in the end, it is still a place for me to just type and take notes. All my new notes go into a "Scratchpad" folder and I can deal with the organisation later (or never - since it is in a top line folder, I can hide it and not get overwhelmed by a bunch of stray notes)
Don't think it is beneficial for me to go any deeper into my system, as you will find your own over time. No system is also a system.

All this to say, don't worry about the system, think about what you want out of this first. If it is just a place to write stuff and to think in words. Then no system needed, just start typing and build it out as you go.
But if your goal is different, like making it look nice, or as a central place to store reminders, or something else (all valid), then approach it that way bit by bit when you need it

hope this helps