Lawns - Kentucky Blue Grass + Fertilizer, or just Kentucky Blue Grass (existing lawn)

Existing lawn, new house.

Obviously the previous owners didn't care at all about their lawn. I'm going to throw some Kentucky Blue Grass down over some fresh dirt.

Should I simply put the KBG down or should I mix it with fertilizer?

Starter fertilizer would be the way to go.

Also in summer weather lawns are difficult to establish.you will need to water regularly and water early in the day not late day or at night.

Depending on how well the seed survives it's fairly likely you will need to seed again in fall.

You will not be able to deal with weeds for "three mowings" or 4-6 weeks after seeding as the weed killer would kill your new seed.Because of time that means no weed killing this summer unless you do not seed in fall which is unclear.

I agree - starter fertilizer and wait for the peak of the summer heat to be past.