I have always enjoyed categorizing and indexing things. Labels, groupings, sections, categories.
There's a lot to be found online on the principles, hows and whys of digital note taking and note keeping. Most of it is primarily concerned with text based content. Text is an accessible and portable medium of expression. Dimensions, length, amount of text per note is not a big concern for digital texts.
How much more complicated it becomes when the source material is physical and the content is of a pictorial nature. A meaningful sorting and grouping is harder to establish.
But. Worrying about an overarching structure is a form of procrastination. An imagined need to know the big picture beforehand keeps you from getting started.
Finding out about Luhmann's Zettelkasten was an a-ha moment and a big relief. The approach Luhmann took for connecting and ordering individual physical pieces of writing is infinitely flexible and expandable. No preconceived classification needed. An open ended numbering system allows you to simply start. Somewhere, anywhere.
This removes an important mental block. Any place is the right place to start because there is no wrong place to start. There's no special weight or importance to note number 1. Even a rhizome has to start somewhere.