The problem isn't the shade, as there are a few grasses that will be fine with 3-4 hours of direct sun, it's the heat and humidity. Tall fescue can tolerate that much shade, but the heat and humidity will be its downfall. Shade will actually help in your case as it will keep the area cooler, but disease will be an ever present threat. If you decide to go with tall fescue you will probably have to use fungicides in the summer, provide water in times of drought, and syringe in the hottest weather.

Here's a hug for you, Mishmosh. You have lots of good advice for people. If you have used Tenacity soon after seeding and it turned it okay, you could say "Although the instructions say thus and so, I have done thus and so at thus and so time and it got rid of the weeds and didn't hurt the grass." That's fine. It gives a personal experience and also alerts them that it's contrary to instructions. Then they can think it over and do whatever they choose. But it's an informed choice. I like that you were trying to salvage their grass instead of just being pessimistic. It seems that everytime someone mentions they have done a spring seeding, all they hear is gloom and doom. True enough, it may turn out as gloom and doom (especially if they're in the transition zone--I think we may as well tell people here to just give up and plant crabgrass and be done with it), but some people have been successful, or at least partially successful, with spring planting.

Excessive irrigation under high temperature can cause more damage to turf than high temperature alone, because wet soils retain heat for long periods and are associated with lack of oxygen." Makes no sense. Moist soil maintain a more consistent temperature (high or low) because water holds heat better than minerals. As the moisture evaporates it cools the soil. So then, does maintaining a shorter height of cut reduce water usage by the grass? The answer seems to be yes. As many of you will remember, back from 2011 through 2014 I lived in an odd part of Texas influenced by the humidity of the Gulf breezes but on the edge of the desert. While we got the humid breezes we rarely got enough rain to grow anything but mesquite and live oak trees. While I lived there I allowed my St Augustine (Floratam) lawn to grow without mowing. The idea was to see if taller grass used less water than shorter grass. The lawn started out low, and I stopped mowing. The grass in the most shade grew up the fastest and reached 32 inches tall within six months. We had been in a drought, so I watered all the grass regularly on my deep and infrequent schedule. We got in inch or so of rain that fall and I no longer needed to water that tall spot. From October 2011 through Feb 2015 when the house sold, I never watered that spot. The weather went from drought to rainy and back to drought. As the grass in the rest of the yard grew up I reduced the frequency of watering accordingly. At the end almost all the yard had grown up to the full 32 inches. I completely stopped watering the normal part of the lawn. It did not need it. Nor did it need fertilizer, herbicide, or insecticide. I never got snakes (in rattlesnake and coral snake country), mosquitoes, rats, or any of the pests people told me I should have. I still had scorpions and tarantulas, but not apparently in the grass. I focused all the watering on areas where the St Augustine was spreading out from under trees into the hotter parts of the soil. Here's a reminder image for those of you who were here with us in 2014.If you look carefully you can see my Chow chow's ears and the top of her tail in the grass. When I sold the house the new owner immediately mowed from 32 inches to 2 inches. I told them to use a string trimmer and bring it down gradually, but no. They had to do it their way. They broke a commercial riding mower in the process. It took awhile for the lawn to recover from the drastic mowing, but it seemed okay the following summer. Now, according to Google Earth aerial imagery, it is dead. I presume they could not afford to water an acre and just let it go. I'm going by that town this weekend. I'll do a drive by and see what it looks like. It should be green with the rain they've had. So my point is that rather than adjusting the deep and infrequent watering approach, my first thought would be to completely stop mowing when the summer heat hits. Allow the grass to get as tall as is practical for you in your situation (spouse, children, pets, HOA, and/or neighbors). Then when the temps cool down or you get more frequent rain, bring the height down with a string trimmer at little at a time. The trimmer goes very fast because you can swing swath of 6 feet or more with each pass. Holding the cutting height is not that hard once you get into a rhythm. In fact I'm string trimming now on the weedy part of my current lawn instead of mowing. I want the grass to grow taller but don't want the weedy bluestem seed heads sticking up. The seed heads seem to be scientifically designed to not mow off with a blade. So I am mowing the St Augustine and weed eating the weeds.

Yes, your soil test is good. Your pH is in the sweet spot. Nothing is deficient. Phosphorus is listed as medium. I don't know which extractant was used so I can't interpret the ppm number. But medium would indicate that it won't hurt to have more but it's not necessary. High would mean don't add any more. Very high would mean definitely don't add any more. The 10% KBG, 90% TTTF (by weight) would give you about 50% of each. It's because the KBG seeds are so small. Since you have picked out your cultivars, you can find out how many seeds they have per pound. Look them up online or call the producer. Gylphosate is gylphosate and the brand is unimportant. Some products have some additives. Plain gylphosate is fine. The mesotrione in the Scott's starter will prevent germination of many kinds of weeds. Crabgrass isn't an issue in the fall. But there are other weeds that will want to grow along your new grass. The mesotrione gives your grass about a month's head start. The weed prevention is short lived but if the grass gets established, it can then shade out weed seeds. You would think with the weed killing beforehand and encouraging weed seeds to sprout and then killing them that weed seeds would be taken care of. It definitely helps. But weeds will come up after seeding. In an even race between weeds and grass, weeds win. They're just stronger. But give grass a head start by suppressing weeds, and grass can win. Urea (46-0-0) is an inexpensive fertilizer. It is very fast acting and you must water it in. Applying 2 lb/k will give you just under 1 lb/k of nitrogen. There is no phosphorus or potassium. It would be a good choice for the late fall application after the grass has stopped growing but before the ground freezes. You would find it at a farm supply or feed store. It can be used earlier in the fall if you spoonfeed it (like 0.5 lb/k every week or 1 lb/k every two weeks). I doubt you want to be spreading anything that often. Or watering it in. But price wise, it is the least expensive way to fertilize. For the part of the yard you're not renovating, a normal sized early fall application and a late fall application will give you 2 lb/k of nitrogen a year, which would be enough for fescue. Leaving the clippings on the lawn when you mow will help fertilize. I would suggest a more complete fertiizer, like your soil test recommends, that is slow release for the early fall and urea for late fall (applied right before rain). For the area you're renovating, use more fertilizer. KBG likes a lot of nitrogen. Aim for 4 lb/k of nitrogen a year, but 3 lb/k may suffice. If you do 4, do 3 lb/k in the fall (August or early September, early October, late fall) and 1 lb/k in late spring. If you do 3, do 2 1/2 lb/k in the fall and 1/2 lb/k in the spring. You can see how much nitrogen you're getting by dividing the N number on the fertilizer bag into 100. That gives you the lb/k rate to get one lb/k of nitrogen. Those NPK numbers are percentages. The Scott's starter with mesotrione (they also have a kind without) is 21-22-4. That means 21% is nitrogen, 22% is phosphate, 4% is potash. Another fertilizer option is organic fertilizer. It would probably be more expensive than synthetic fertilizer and you have to use more product. But it may be something to consider. There is Milorganite that you can buy in a bag most anywhere. But grains can be used for fertilizer: soybean meal, alfalfa pellets, cracked corn or cornmeal, cottonseed meal. I used 25 lb/k of cracked corn this spring and I got 150 lb for about $25 which took care of my 6k yard. Dethatching and scalping will suffice. The light frequent watering to keep the soil moist during weed killing and seeding is just a few minutes, like 5 minutes or so. The goal is to keep the surface moist without puddling or runoff. One inch of water a week is meant to supply water 6 inches down into the soil. You don't need it 6 inches down at seeding. That's for later on, like next summer when you want to keep the grass alive.