Thanks for the quick reply. Its not really on too much of a slope, but i tried using a broadcast seeder and didnt have much luck with germination. I am just trying to fill in the thinner areas.

The key to germination is to keep it moist. It has to be watered 3 times a day, 10-15 minutes at a time. You don't want to soak the ground, just keep the surface moist. Depending on temperature, fescue will take up to a week to show signs of germination. KBG will take 2-3 weeks. Covering the seed with peat moss or clean grass clippings will help retain moisture.

I have about a 1/2 acre property that i will be overseeding. How soon after fertilizer/post emergent weed control can i seed?

There's no restriction on fertilizer. The weed control varies depending on AI, instructions should be listed on the label as far as how long you have to wait before seeding.

Can I aerate and the immediately use an overseeder, a slice seeder? Is that too much for my lawn to overcome? I had fertilizer put down about 2 weeks ago. Do I need to put down starter fertilizer too?

What are seeding and what kind of grass do you currently have?

Compared to slit-seeding, any additional adverse turf pressure from aeration is minimal. Breaking up the cores with the slit-seeder is a "plus."