I don't know for sure if you found the right numbers, but they sound about right.

You can use it on growing grass. Starter fertilizer has more P because that is supposed to help new roots.

Use 5 lbs per 1000 sq ft of lawn to get 1 lb N per 1000 sq ft.

For future fertilizations, before buying the fertilizer, find out whether your soil is deficient in P and K first. Depending on where you live and your soil conditions, you may be able to buy something that has only N (such as ammonium sulfate 21-0-0 or urea 46-0-0).

Buying fertilizer with P when your soil doesn't need it adds to water pollution. Also, if you don't need the other stuff, the N only fertilizer is considerably cheaper. The brand name is less meaningful than the NPK numbers.