Chinch bugs or grubs? It does not look like typical water stress since the brown spots extend far from the concrete sidewalk.

You're ok for this year, but a quick bump up of one notch on your mower would help green it up. This time of year you get a lot of Brown stem, but it's too late to scalp. Next year do a proper spring scalping & you can keep the stems away until September if you stay consistent

I'm looking into top dressing my yard next year with just sand for leveling purposes, do you think that we'll help those thin spots to thicken up and grow better or should I hit those spots more with the aerator and fertilizer?

And my deck mower is the 2nd notch down from the top when I mow. It's the number 4 spot on my zero turn.