Sweet William is a biennial, so chances are it won't bloom this year. You might consider buying a potted plant and sow some seeds as well. You are okay with sowing the balsam and baby's breath now. Nigella/Love in a Mist is an annual and should reseed easily, check to make sure you aren't weeding them out.

When I grow sweet william from seed, I start it at the same time I start pansy seeds, in late summer. I set them out in the garden in fall and they bloom the following spring. Starting them now, especially outside, will virtually guarantee that they'll die before they ever bloom, IF you even get germination.

Are you positive that baby's breath and candytuft will do well in your climate? They don't in my zone 8a climate. I have had limited success with candytuft, but it doesn't persist more than two or three years. If you're going to the trouble to grow perennials from seed you at least want to know that they can make it.

Seed starting is a rather exacting science. Yes, some plants are super easy to start outside, especially if you sow enough seed: zinnias and marigolds certainly fall into this category. Balsam, too. However, most seeds, in my experience, require proper timing, proper light, proper temperature, and proper equipment to be started successfully. Perennial seed is rather costly. If you don't have the time to give them the attention they need, you'd be better off to purchase one or three plants, and then divide them as time passes.

I would suggest that you spend this season reading and learning about seed starting, sow some easy seeds in your garden for this year, and then work to be genuinely ready to give it a try next year. I hope this doesn't sound too negative, but I truly believe you'll have a much better chance of success if you start simple and work up to the more difficult stuff gradually.