I've never had much luck growing flowers from seed with the exception of Sweet Pea, Nasturtium, and Morning Glory. Either they don't germinate or they end up stunted and don't get flowers until the end of August. I think a big part of my problem is that I don't know when to start them and whether I should start them inside or wait and direct sow them. Last frost is supposedly in late April/early May, we usually plant stuff outside on mother's day weekend, so around May 11th. I prefer starting seeds inside but know that not all types of plants do best this way. So what can I start inside and when should I start them? What should be direct sown?
These are the seeds I have:

Marigolds
Sunflowers
Zinnia
Sweet Pea
Nasturtium
Morning Glory
Tithonia
Larkspur
Chinese Lantern
Bachelor's Buttons
Alyssum
Foxglove
Portulaca
Flowering Cabbage
Gaillardia