great that you are continuing to capture constantly, even outside your weekly review!
Actions should always land in next-action lists, even when related to projects. You don't want to keep action reminders buried in project support.
I would typically put something like "buy stapler" either on an @errands list or @computer if I'm buying it online. You don't want to miss an opportunity to move your projects forward just because you didn't look at that project's list of actions.
Whether you want to have some way to see within your system which actions are related to which project, that depends on personal preference and the capabilities of the tool(s) your using.
Personally, I find I don't need to keep detailed plans or outlines of actions for most projects. At weekly review time, just having the project on my list triggers planning and identifying the necessary actions to keep it moving.
What I will keep in project support are lists of
future actions: Things I know I need to do for the project but I
cant do yet
. Keep in mind that you can have multiple next actions for the same project, as long as you can do any/all of them simultaneously. For example, in your office space example, you might need a stapler but also want to replace your office chair. You dont need the stapler before you can test out chairs - so you could also put on an errands list - "test out chairs at office supply store". Those are both next actions for the same project.
Hopefully that helps