I'd be wary of tilling. After you till, when you level it, there can be airs paces and so forth and as it settles, these can end up leading to uneven ground. Tilling in compost can exacerbate this, since the compost will continue to break down, and unless it's distributed exactly evenly, you'll end up with even more uneven spots. The best thing to do is to have it graded, but if you don't have the money, that may be out of the picture. Some people have done it slowly by core aerating the lawn and raking cores to low spots and/or spreading sand no more than 1/2 inch deep in the low spots. Planting in the spring can work, but you'll often end up losing grass in the heat of the summer because it isn't well enough established. If you must seed now, you'll need to be more vigilant about watering in the summer. You may end up needing to overseed in the fall, also. If you use KBG and enough makes it through the summer, it can fill in as long as you don't have huge bare spots. I know that a lot of seed mixes you see in the store are a mixture of KBG, fescue and rye, but I think you're probably better off going with just KBG unless you have areas that are excessively shady. If you want to get the seed that will look the best, here is a list of KBG blends by state. If you want something that will look pretty decent, you can buy seed at a hardware store or garden center.

The easiest way to ID weedy grasses is from the inflorescence, the seed producing stalk. Compare your weed to Dallisgrass, you could also try asking on the grasses forum or Name That Plant. Good luck!

By all means, poison the bejeebers out of everything. The stuff you bought is right for the job. I used to live in SD and we had those same weeds back then. Good news: after you put in a lawn, mowing will chop down any new weeds from seed, so they will not be able to reseed continually. You will win. If you go to Google Images, and type in BURR, you will find out that your weeds are indeed BURRS. Plain old Burrs. Not hard to kill. Mow it down, rake it up, throw 'em away, poison the whole area, wait a few weeks and put in a new lawn. Since you are starting fresh, you might want to consider adding an attractive organic garden for fresh veggies, fruit trees, or just attractive plants. HERE is what I did in my own yard, including how I built a new lawn with grass plugs and regular watering. My back yard orchard is almost pest free, weed free, fertilizer free, chemical free, and very low maintenance. I even got free mulch from the county! Hope you enjoy the video. But do not despair. You control the destiny of your property. I can tell that you will do good things. Please be sure to include photos or video as your plans take shape.

The poison ivy will need due care when removing it, and it will need to be bagged and discarded in the trash, it is not something to compost or otherwise use again. The rest can be mulch mowed, fairly frequently, to be kept under control. If the area is to be used as a garden then you need to learn more about the soil and what it needs. Start by contacting your state universities Cooperative Extension Service about having a good, reliable soil test doen so you know what your soils pH and current nutrient levels are and also dig in wioth these simple soil tests, 1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top. 2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up. 3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart. 4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell. 5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy. to see what else that soil might need.