I don’t see anything in the plan for weeds or fertilizer.
Once you drop seed it will be a good long time before you can use an herbicide to kill weeds. After germination and a couple of mowings, there may not be time until next season (don’t know your climate well).
I would spray for broadleaf weeds a week or so before you plan to begin aerating and seeding. Herbicides are cheap. Getting rid of the weeds chemically is a short cut to crowding them out with the good turf you plan to establish. It will also give the new grass more of a chance.
I would get a complete fertilizer (mineral type) down right now to beef up the 40% they have. Somewhere around 0.75 # N/M – means you need around 300 pounds of nitrogen from whatever formulation you use to cover 9 acres. Giving the fertilizer 7-14 days to work before addressing the weeds will make a big difference.
If all they did was the above, mow properly from now, and fertilize at least twice a year and spray for weeds once a year, they would see a big improvement. The work you described will make an even greater difference, but fertilizer and weed control are where I would begin.
When you aerate and drop seed you will have much better results if you use a starter fertilizer. I would do both if they will go for it: 0.75 # now and a starter fertilizer, such as 18-24-12, at 1 # of P/M when you seed.
By Thanksgiving these soccer will look much better.
What is difficult with many of these places is changing the way they look at things. Often, they think renovation of the type you propose is the end of the story. As we know, continuing maintenance is important.
If you get this established and introduce them to good mowing practices, they will want the fertilizer, weed control, and more aerating next year to protect what they have. If they will not or cannot go for the whole plan this year, try to get them to try the full plan on one field and let the results speak for themselves.