Are you planning to go just with plugs? You might want to give them a more mature spacing, rather than really dense, and then mulch and treat the area with a pre-emergent herbicide this first year (Finale and the like or corn gluten meal). This will get the plantlets off to a good start with minimal weed competition.

CJ

I agree with CJ. Planting them too dense will be a lot of competition and they won't grow as quickly. As far as design, what do you like better? The natural look or a slightly more traditional look? If you're in a city, I suggest the more traditional garden look, with plants in groupings. Your neighbors will have fewer complaints this way.
nick

Planting 12" apart is a good rule of thumb unless the particular plants will get exceptionally big. I've planted plugs directly into a lawn and this has worked out well. Turf grass doesn't compete all that well with taller plants and will eventually be shaded out or outcompeted for root space. After the first year a burn can wipe out much of the turf and weeds. Since you've already covered the area with newspaper, why not plant directly into that and mulch? I've done that too and it looks very attrractive.

Well, thanks for the responses so far. I have no neighbor worries here in this rural area. That's why I love it so! But I am not sure if starting a fire in my front yard would be appropriate. The houses are not that far apart. I was originally planning on a more natural look, but the space just seems a little small to pull it off to good effects. 12" spacing is probably doable and I do plan on mulching between the plants. How fast will first year plants fill in? I realize that only a few species might flower the first year. Does the foliage grow up much or just roots growing? I am new to many things here.
Thanks for your help!

Each species is different. Last year I started a number of plants from seed. Side oats grew into small plants and flowered. Royal catchfly just sat there as a small rosette of leaves the whole year. In contrast, I had yellow coneflower get quite big and flowers by late summer. Sky blue aster bloomed from plants that I started in February. Compass plant just gets a few leaves, the largest about 12" the first year. Bigger plants like compass plant, rattlesnake master, false wild indigo, leadplant, ect should be given 2 or 3 feet spacing minumum. If you mulch between plants and want them to stand out individually space them even more. On the other hand, keeping them close will produce a dense mass of roots that will stop weeds from invading.

Thanks, Lycopus!
Yes, I will have a variety of plants. Does anyone know how fast any of these will reach mature size? Bloom first year? Crowd out other species? Is this too many species for my meadow (20X25')?
Ratibida
Liatris
Agastache scrophulariaceae
Aster umbellatus
Coreopsis tripteris
Vernonia noveboracensis
Verbena hastata
Sporobulus heterolepis
Monarda fistulosa
Monarda citriodora
Silene regia
Turk's cap lily
New England aster
Big bluestem
Little bluestem
Showy goldenrod
cup plant
milkweed