Still without my land line here but wanted to get back to your thread and proposed field.
I am within days of completing a baseball field that I began 13 months ago. Many. similarities to your project: extremely poor (unusable) original condition, no permanent irrigation and undertook the job as my contribution. In addition to neglect, misuse (football team used this as its practice field a few years ago), we were faced with an unmanageable 14" layer of river silt that was placed uniformly over beautiful native sand throughout the park. Regretably, the school had paid TG throughout 2007, bringing it to the condition presented on my first day
ver 100 large geese nesting and calling the ballfield home, all desireable grasses gone entirely or accounted for less than 5% of the cover, heavy grub infestation, dozens of active moles, grown over infield skin and base paths. Crabgrass and lots of it had taken over the infield and outfield. Batters box and pitcher's mound had to be completely rebuilt after tearing out big lips. In time, we got rid of our pests, had irrigation installed, rebuilt skinned infield surfaces and grew new grass (blue-rye mix).
When you say "grading" I think the worst. On my project, we disturbed the surface much more than was necessary. This caused much extra work but no real benefit. Once you disturb the surface, whatever is in season will begin to grow back. Chemicals can provide a window of time to help get your field up and established in spring even though convention suggests late summer-eaely fall is a better time.
At this time of year, I would encourage you to do any frainage work that needs to be done and let that help you get established in spring. Also, if you plan to amend the soil that could be completed yet this fall.
Tall Fescue is coarse, durable, and resists drought well. I think I would use a traditional. Athletic field mix of ryes and blues and hope for long term average good growing conditions. Let Natural Selection do its thing. Sounds like the in-season time for field hockey is fall, whis is a forgiving time of year for cool season turf. Someday they may add irrigation as they did here part way through the work.
Good luck with this noble project. I will be watching this thread and look forward to updates on your decisions, progress, snd setbacks. I can provide photos and more specific information once I get back online, if you are interested.