For ground prep I did two spring spraying with roundup. The second spraying included some Crossbow to take care of a bunch if Ironweeds that emerged after the first spraying. It also included a very small amount (4 ounces/acre?) of Plateau. Even with all this, there was still a lot of stuff that came from the seedbank - some I liked and some I didn't like.
I think an improvement for me would have been a late summer spraying and then another one (or two) next spring. The more you can deplete the soil of things you don't want the more likely what you do want will do better.
My seed were drilled, and as stated before, mine was done with a mixture of forbs and grasses. When you do this, the forbs will show up mainly in the first two years and start to disappear as the grasses form their stools. You can disk and bring them back, but you also bring back all the things you don't want in a wildflower plot (such as Canada Horseweed).
It depends on just how "pretty" you want it. If its for deer, then you can get by with less work. If your trying to please a woman - oh well, never mind...LOL.
Plateau was made for Prairie establishment. It's very expensive but it will take care of a lot of undesirables such as Johnson Grass. It will also hurt Switchgrass at some levels, but there are a tremendous bunch of wildflowers it won't harm at the recommended rates. If anyone has Johnson Grass (glad I didn't) you are in for a job ever getting rid of it, and it will take over about anything else.