I don't follow rules well so I try
not to impose them on others
Fling daily, save for an application and/or bring them home from a coffee shop -- all good answers.
What I just read also suggested making a coffee solution out of the used grounds and applying that as well.
I not an expert on NPK but also just read cheap options - fruit/veggie compost, manure, ashes, kelp meal and rock dust.
I would do what was cheapest/easiest.
You could make tea out of the manure compost. Depending on its break down - fresh out of the horse, six months old or 3-yr old black gold - will depend on if you treat it like old timey manure tea or highfalutin compost tea.
I think you mentioned you had high clay soil. That is good. Additions of organic material and decomposers thru tea/manure/compost will start to transform this into better soil.
My thoughts are that you do these things and then if you like your lawn - go with it. You really don't care about the numbers unless something isn't growing right.
Worm Banner -- worm composting is the best and easiest way to take waste and put it to good use. I turn my coffee grounds, banana peels and paper towels into steak. I buy the steak with the money I save by not buying fertilizers, potting soils or yard amendments. I like steak.