When the fescue is 3" tall, the KGB will likely have germinated. Or at least most of it will have. It will take more than a month for the fescue to reach 3" tall. You can put down starter fertilizer at any time. It won't hurt the grass. I usually put it down with the seed. The only thing about fertilizer you need to be concerned with is not to put down fertilizer that has weed control. Depending on the particular weed control, it will either prevent the seeds from germinating or harm the young grass. It's a good idea to lightly cover the seed with dirt, top soil or compost. It helps keep the seed wet and helps keep the seeds in place.

Since Milo is organic you will be fine to go ahead and put down starter fertilizer when you seed. But, it's been recommended on these forums to only put down half the recommended rate of starter now and then the rest in about 3 weeks.

It might have helped to vac the lawn or mow it with a bagger on before doing the overseed. But, my experience has been that the dethatching slit seeders with a seed hopper on the back of the unit do a pretty good job of getting the seed down in to good contact with the soil. In other words, it will germinate ok even with some "thatch"/dead grass kicked up by the unit in the process. But, you probably need to do a search here on proper watering of grass seed for best germination. There has been a lot written about it. But, in simple terms, for about three weeks you want to follow the Goldilocks rule. "Juuuus right". Not too wet, and especially never too dry for too long once it starts germinating. depending on soil, sun, wind, cover (like your thatch), rainfall, etc you might have to water as much as three times a day, lightly, or hardly at all (if it stays cool, wet and overcast). Basically, you just have to WATCH it. If its dry, water it. Think mother hen for about a month. Good luck.

The West Michigan Grass seed mix is a combination of Blue Grass, Perennial Rye, and a Fescue so more than likely there is a similar mix available in your area under a different name. The proportions may vary but the one I like best is 30 percent Blue Grass, 30 percent Fescue, and 40 percent Perennial Rye.