Wildflower Install Help - CT 6B-7A border

Hi All!
Located in Connecticut on the border of 6B and 7A. I spent most of my summer removing a bunch of shrubs and hedges that were vine-chocked and just a mess. I have a sizable area that I have been solarizing for the past couple of weeks (month and a half starting in October). The area is about 10'x25' and is covered with 3.5 mil plastic as I write this. The area is also right by a swamp maple tree, so most of the soil is compact and heavily rooted.

My question is, after I solarize it, I was planning on adding about 1/2 of soil to the bed. Should I try to rake out the soil or loosen it as much as possible (I do have a tiller, but felt that I might bring up unwanted seeds after I solarize it. Also, would you put down cardboard or paper mulch before the soil (I have a lot leftover)?

I am planning on planting some prairie moon mixes and seeds for my region.

Thanks!