I think the recommend rate is 1 teaspoon and 2 tablespoons soap to a gallon of water as a spray.Have not had to use as a soil drench so have no idea as what the ratio would be for that.Overall I think neem is pretty safe to use.
Just been doing some reading and the horticultural lot suggest just 2% neem oil added to water as a foilar spray with an emulsifier. I'm using pure olive soap as an emulsifier adding about a teaspoon.
Seems very effective. Adding a teaspoon on baking soda to the mix helps with powdery mildew too. More info google 'Horticultural oils'