I've never started sunflowers indoors, because they grow so quickly direct sown outside. I've always direct sown them after my last frost date because I don't like having to harden things off that were started indoors. They like a warm, sunny, well-drained but a bit moist location. If you direct sow you just plant more than you think you want, but reserve some seeds to resow if necessary or stagger the sowing.
I love the look of a large number of big-headed sunflowers, but they don't look so hot after you get a summer storm. Wet soil and high winds makes them tip over and uproot quite easily. Now I only plant the giant ones if I can put them right next to a sturdy structure to tie them to.
A few times when I grew the "Russian Mammoth" or "Giant Grey Stripe" varieties most of the seeds didn't have any hearts in them. Lot of bees were on them all summer, but the seeds were all pretty much duds. Now I think I like the smaller head branching sunflowers better. They aren't as tippy and they look better to me.
Other easy plants with seeds the birds like a lot are coreopsis, zinnias, and echinacea. Stay away from the poofy double-flowered varieties of all of these though. Butterflies, bees, and birds want easy access to the nectar and seeds.
