I am taking over my own lawn work after deciding that I could kill off
my 25 y/o sod yard at least as efficiently (and much cheaper) than my
lawn service. Being an newbie, I have some questions.
In Central Indiana, when should I put down the fertilizer (and
what kind), the weed killer (I prefer granular but could do liquid if
there is any consensus one is better than the other)? I am leaning
toward fertilizing and then weed killing. Any real reason to do it in
two steps? How much time between the two?

I am thinking about doing some reseeding. Currently I am considering
just broadcasting the seed. Does that impact on the timing of the
fertilizer and weed killer.
The area is mostly clay and I am told the original developer sold off
most of the top soil. Over about the last five or six years, I have seen
the sod markedly become thinner and thinner to the point where there are
now bald spots. However, this hasn't been terribly consistent with some
areas that I don't have to mow but every 2 weeks abutting areas that I
need to mow weekly. Because of the clay I have aerated every other year.
I don't know if this makes any difference in the suggestions, but
I thought I'd throw it in.

--
"Even I realized that money was to politicians what the ecalyptus tree is to koala bears: food, water, shelter and something to crap on."
---PJ O'Rourke