I'm in zone 6 up in the Rockies, and we wait until Mother's Day to put things out in the garden. With seeds, I suppose we could go a week or two sooner, since they may take a few weeks to sprout, anyway.

But your coastal zone 6 may be safer sooner than my zone 6.

I direct sow zinnias & marigolds May 1st or thereabouts here in Northern California. They will only sprout when it is nice and warm.
Alyssum is reseeding (sprouting) now.
The others probably work in April.

dannichase, as you can probably tell, most of the plants that you've mentioned prefer to have (or must have) the soil (not the air, but the soil) a bit warmer before sowing. The alyssum is the exception, as it is a member of a large family of cool season plants (Brassicaceae), along with broccoli, cabbage, etc.