I didn’t know much about Zettelkasten until I tried using Zettlr,

I quite liked Zettlr and I must say I had very enriching discussions with his dev, a few years ago. He had a real good vision & understanding of what a Zettel-like app sh/could be. Imho, it was leagues ahead than all the others apps… but still not as functional, for me at least, as my simple pile of index cards.

I’m split between physical vs electronic Zettel

Privacy (and control over my data and who can access it) is the main reason why I remain analog (even more so with something as intimate as what I think on sometimes very delicate subjects: I know I cannot trust digital and even if I can (Linux is great, I would not want to go back to Apple) it can still bug and fail me at the worst time), but like my previous paragraph may have hinted at I never was hostile to digital per se. I became hostile when the telemetry/tracking/privacy soon to be outlawed nightmare began and when the subscription craziness became the norm.

I’ve started using just a regular little notebook in my pocket for taking notes,

I do that too, save that I use an A6 notebook (like my index cards) and write on the long side, so I can simply remove whatever page I think is worth it, add a number and index it to store it in the Zettel. Being lazy as I’m is a huge boost in finding simple solutions ;)

Can you tell me more about how your organize your physical Zettelkasten’s indexing/numbering?
Like do you bother to number each card individually so you have an index somewhere that has each card topic written down, or do you just give them general numbers for a topic/category and then stuff them in the box any order within that category’s section?

Each card has a unique number (it’s required for the Zettel to work), the numbering format itself doesn’t matter much if at all. It just need to be unique (which is easy to do) and it can be anything. As a matter of fact, over the time my ‘numbering scheme’ changed more than once… without any issue and without the need to renumber the existing notes. I would not want to do that ever.

What truly matter is how you index it, and how your cards can be linked to one another.

I have an index for whatever notion I work with or I’m interested in. Some of them have a single entry under their first letter followed by numbers pointing to the relevant cards. Say, Once an entry tarts having too many cards linked to it, I will strike it out and put a link to a new index card, that will be dedicated to that specific topic. An example will make it clearer:

Say, I have a ‘D’ card listing anything relevant that starts with a ‘D’ (duck, dance, dirt,…) but then I also have a “democracy” entry that is starting to grow too much. I strike it out on that firs card, add a link to “DEMOCRACY (D)” (which is a new card with that title that I will add to my index) and I put all entries related to democracy on that card (and then on a second one and so on as much as I need to). If the I have say a growing number of entries for “End of democracy” I will simply strike it out on the 'DEMOCRACY (D)" card and create a new one titled “END OF (DEMOCRACY) (D)”. The ‘(D)’ helps me quickly remember to put back it back at ‘D’ (and not at ‘E’ like I would be tempted reading its title). That index, plus the author’s index I also use, is the real workhouse of my Zettel .

I started my Zettel using a few academical categories (History, philosophy, Physics, Biology, Literature and stuff like that, I even created sub categories, for countries and era) but in the end it’s more noise than it’s useful as I will waste time trying to decide where I could put each new card which serves no purpose at all as I could simply have started numbering all of them from 1 to whatever thousands. Like I said, what really matters is the index (where categories already exist and have a purpose) and then it’s the linking between the cards. Those links this is where the magic happens as far as I’m concerned: the index leads me to the specific info I’m searching for, say ‘Democracy’ but then while I’m reading all indexed card under that entry, I will often find direct links to other cards and that can trigger real unexpected associations.

Like, I remember having links to ethology under some of my cards related to Rousseau Social Contract, while those have links towards some prose or poetry (they too have their place in my Zettel) that will themselves point me back toward stuff related to, say, Augustine, or some passage from the Bible or to Plato, or a painting that will itself point me to some comment made by Proust on the same painting. Or maybe to some notions about light and wave length in physics or even to ship building in the XVII & XVIII century in Great Britain, or in France, that may point me back to ship building in Antique Greece and in Egypt too, that could then lead me to… other stuff.

it’s rich and to me it really feels like having a conversation with a smarter version of myself.

I’m sorry, that’s along reply… I really should write a blog post instead.