So, what are you looking to accomplish with summer plots?
Just building soil, to improve fall plantings? Then don't worry too much about the Johnson Grass...it won't co.pete with fall plantings, as it gets killed by first frost. Nuke the ground with roundup, then just plant cheap generic beans, sorgham, and millet to build soil and suppress some of the weeds. Keep doing thus for several years and you will make progress.
If you are wanting a beautiful summer plot to feed deer with little weed competition because you plant to leave the corn or beans standing, you need to go with a preemergent such a meetoachlor or the like plus roundup which needs to go down a month before the RR seed. Then come back with roundup to clean the corn or beans after they are a foot tall or so. Now this is assuming you are drilling. Your local coop agronomist can look at the fields, see what type of competing weeds are most problematic, then make the suggestion on exactly which preemergents to use.
The problem with NWTF or Quail Unlimited is that they are nit guaranteed to get in the seed they expect... so you can pre-order, wait all spring long, find out late May they aren't getting seed, then you are left scrambling at local seed stores buying whatever was leftover. That happened to me 5 years ago... joined Quail Forever, ordered seed for 10 acres. Then, sorry, the distributor didn't deliver... here's your money back.
I want the seed sitting in my garage by May 1st... you won't get that with Quail Forever, even if they get their seed in that year.