8 acres does not need a beast of a tractor by any means.
35hp is really plenty, and if you'd like to save time to the max go up to 50. Beyond that is a waste of money & will just have a bigger turning ratio that you don't need.
Many guys use even smaller, but for a planting of 8 acres I'd want 30 as minimum.
And a 6-7' disk should be easy to get used if you check around at some ag sites.
A chisel plow for better drainage is a good idea as is a drag for a much smoother & even seed bed, or to just lightly cover over the seed of a clover plot if you were to decide to expand what you plant for.