You'd have better success if you did it in sections and smothered the grass with cardboard and some sort of mulch to give the seedlings a better fighting chance. Or you could consider herbicides if you're in a hurry. My sister has also used old pieces of carpet to smother weeds. I love the idea. Good luck.

Martha

Thanks for the advice. I've decided to go with multiple applications of roundup for this year with some more careful planning for next year.

Do you know when your mowing will take place? I like to have things mown in the late fall or late winter (although this isn't the best thing for wildlife) and then not mow again until July or so. This timing isn't great for fall blooming native plants, but keeps the grasses under control and looks neater imo. I'm trying to avoid having goldenrod take over.
Most of the later plants like bluestems and asters come up again and bloom normally, just a bit later and shorter.