Things to do this fall and in what order?

[David W]

I am fixing to spray grass/broad-leaf herbicide and it says to wait 3-4 weeks to re-seed. Okay no problem, but I also want to de-thatch and aerate as well as over-seed in the coming weeks. And finish up with Proscape Mesa 25-2-5 for the fall fert?

Is there any benefit to aerating or de-thatching before spraying for the weeds or am I better off waiting the 3 weeks and over-seed at the end of September?

Any helpful advice would be great.
Thanks

[David W]

Oh and the turf are lawns that were sodded in the past 1-2 years. Good denisty and just a few thin areas.

Just want to stay on top of the weeds and keep these lawns nice and thick fescue.