You are almost in my back yard. By new lawns do you mean on bare soil? I am not sure if a slit seeder is the weapon of choice.
Anyway, around here a mixture of bluegrass and perennial rye is most often used. Try to find a mix of 80 percent blue and 20 percent rye. The rye is more aggressive as a seedling and will tend to crowd out the blue--so you end up with about a 50 50 mixture. One of my favorites is Lesco's "Athletic Blend". (not the ratio I would like.)
Begin when the grass greens up in your neighborhood--about April 15.
Be sure to not guarantee anything as you cannot control weather or customer watering.
Be sure to use starter fertilizer. And follow up at 3 weeks and 6 weeks with a high nitrogen booster feeding like 24-0-11 to stimulate maximum growth and rapid fill-in.
You will need plenty of weed control for most spring seedings...send me a private message and I can set you up with a weed control and or fert program.