Yes and no. The biggest hurdle is using emacs, org-mode itself is just a rather simple plaintext format. But as a beginner it’s best if you just consider emacs to be a kind of text editor like mousepad or notepad. If you just install it, it will basically look like a weird version of those programs. What might seem intimidating are all the keybindings long-time emacs users regularly throw around. You can just ignore those for the beginning.

But emacs is also extremely well-documented, though. Your biggest aides as a beginner would be “C-h i”, (pressing control + h, then i) to bring up all info manuals installed on your machine, and the various ‘apropos’ commands, which I usually just call through ‘invoke-command’ “M-x” (meta key + x). The emacs manual is pretty good. I know lots of people start with fancy emacs distributions. I would however suggest just starting with plain emacs and keeping the menu bar open for the first few months.

Disclaimer: I do almost all of my work in emacs. And my comparisons to other methods of organising yourself are a few years old.

In my eyes, org-mode (https://orgmode.org/) is the most flexible FOSS option if you’re willing to use a laptop running emacs for most of your organising needs. I’ve been using it for years for all of the demands you describe.