I used to have more complex systems for tracking projects and tasks, and I would keep this separate from notes. However over time I realized that the overhead wasn't worth it—more fine-grained planning can give a feeling of progress as you check things off, but it pales in comparison to entering a flow state on a hard problem. On the other hand notes turn out to be super valuable over time, even if they are rough and incomplete. So in order to minimize overhead, I flipped the script and optimized for note-taking with todos tacked on in the lightest weight possible.
Today I use Workflowy for this system, both professional and personal. Being able to zoom into an infinitely nested list for focus and then search broadly with the hierarchy fully visible in the results makes for a very potent combination. Action planning then falls out of the system naturally without significant extra effort.
At the top level I keep major life category buckets (work, family, finances, etc) which never overlap. Within each category I make entries in a reverse chronological fashion, with explicit dates if they represent a discrete event like a meeting, or without dates if it represents ongoing work or brainstorming. At the bottom of each category is an "Archive" entry, where I will periodically sweep old items from the bottom of each category. These swept items are also maintained in reverse chronological and bucketed monthly/quarterly so the lists never get too long. Within that structure, whenever a concrete action needs to be taken I tag it #action and then cross off when it's done. My planning is now just to search for #action, and one every week or two audit the list for actions I no longer wish to complete.
The beauty of this system is it's super lightweight and flexes really well to IC, management or personal task.