When designing your system, you can probably be less specific than you think.
This post details the single area that managed most of my life for me for almost a decade. It worked just fine.
Remember, by the time you’re in to a category —
15 Technical, say — you’re already two levels deep in to a very organised hierarchy. That’s probably enough. Scanning that list for
15.34 List of server logins isn’t a burden.
What I’m saying is that you might not need to go so deep. In the first instance, try to avoid this:
10-19 Technical 15 Remote login details 15.01 List of server logins
…because you might find that there’s very little else in that category. Aim for categories that catch quite a lot of stuff, and if you find this isn’t working, break them out later.