If you use CGM to stop the crabgrass from germinating, you'll be stopping all grass seed from germinating. Fall is usually a better time to plant grass seed, anyway, at least for cool season grasses.

If you want to sow grass seed in the spring, don't use pre emergents. There is a chemical pre emergent that will suppress crabgrass but let the desirable grasses sprout. It's called Tupersan or Siduron (the first is the brand name, the second the generic name). But since you said you want to be organic, that's not an option, so you should either delay sowing new seed or skip the pre emergent.

Where in the world are you?
What is your soil like?
What is the level of organic matter in that soil?
How much water can you expect to have diring the growing season?

east tennessee, poor-clay soil, i've done a lot to the soil, i can't find last years soil test results but i'm workn on gettn it tested again right now. spring water should be available in rain, but i have to water a lot during the hot dry summers.

In Tennessee you might have both the annual and perennial Crabgrass and how you treat them is somewhat different. Check with your University of Tennessee USDA Cooperative Extension Service people about whether you do have them. The annual crabgrass grows from seed when the soil gets quite warm, that seed will not germinate in cool soils. So the best defence against annual crabgrass is a good, thick turf, cut high (shades the soil so it stays cooler), with the clippings recycled right where they are cut (helps provide a mulch that also helps keep the soil cooler).
Turf grasses deserve the same soil you would grow roses in, a good, healthy soil well amended with organic matter that is evenly moist but well drained.
If you apply the CGM too early you will adversly affect the germination of your prefered grass seed and it will have no affect on your crabgrass seed, so if you do use this, very expensive way to control the crabgrass, wait until after your newly seeded lawn is up and growing. I'm not too sure about east Tenessee but crabgrass does not germinate around here usually until late June to early July, and by then your turf grass should be up and really growing.

Here is a link that might be useful: UT CES