To get the best performance, I would suggest not using commercial
fertilizers, but an organic program with only emergency resort to any
chemicals such as fertilizers or herbicides. It sounds like you're
trying to maintain a fairly large lawn with golf-course quality
grass-only appearance, which is not very feasible - or good for the
soil underneath. Allowing some clover to intergrow, weeding pernicious
weeds by hand, and making sure to 1) let the grass grow at least four
inches, while never cutting it less than three, and 2) making sure your
mower's blade is always super-sharp are the two best ways to maintain
healthy turf.

Using this system, plus an occasional cheat of a 1/4" of compost (from
my community's recycling program, not dirt-cheap but cheaper than
fertilizer!), I was the absolute despair of my next-door neighbor, who
was retired and spent most of his time working on his lawn.... mine was
always greener, despite the fact I spent much less time fussing with it.