No you are not going about it correctly. Not to be harsh, but whoever you are listening to or are reading, stop it! I'm not sure where to begin, so I'll just try to cover it all.

RoundUp is not a preemergent and has no residual preemergent barrier effect. Roundup kills living plants and does nothing about seeds.

Rototilling the yard might be appropriate for you but ONLY because of the rocks. Generally rototilling would have been the worst mistake in your plan. Whatever you read that suggested that...you can just disregard everything in that article or book, because they don't know what they're talking about. For rocks there are some machines affectionately called clinkers. I'm not sure what their official name is. They rake the soil about 2-3 inches deep picking up rocks and depositing them on a conveyor belt while allowing the soil to sift back through the conveyor belt. The machine rattles with all the rocks and metal stuff so it's called a clinker. If you can find a clinker for rent within a hundred miles, I would be surprised. What you can do is rake it up yourself, without rototilling, and hand pick out the rocks. Or you can hire some laborers to do that. It's probably worth it to hire it done or hire them to help you do it. If you rent a rototiller, set it to only minimally dig into the soil. In fact you might be able to rent a dethatcher, power rake, vertical mower, or slit seeder to get a better effect. Those machines all have vertically rotating bladed that can be set to dig into the soil at a specified and controlled depth. Rototillers are completely uncontrolled at best and dangerously uncontrolled at worst. Not only that but they cause your soil to become bumpier and bumpier starting now and continuing for 3 years.

Never use manure in your garden. First of all it stinks. Secondly it stinks for weeks and weeks (and weeks and weeks). Now if you really meant to say, "composted manure," well then that is called compost and is never referred to as manure. Compost can be distinguished from manure because finished compost smells as fresh as a forest floor after a summer rain. Your nose knows when compost is finished composting. If there is any subtle hint of manure, or mold, or a rank, dank, sour, ammonia or anything that does not smell like fresh soil, then it is not finished composting.

As for the seeding part of your plan, it all depends on where you live. If you live north of Alabama or in the mountains, you may be have time to seed, but that window is rapidly closing. Spring is a poor time to seed new grass for a couple of reasons. If you can do it now, do it. If you live in the south then neither now nor spring is the right time for seeding. However if you want to put down sod, you can do that now or whenever in the north or south. So, where do you live? If you live in a suburb of SoCal, then please be sure to name it and not just say you're in SoCal. There is waay too much variability in climate and soil in SoCal to give blanket recommendations.

Having said all that, have you asked for estimates from landscapers? They will bring in a tractor with a box blade to scrape the surface. The box blade takes out all the weeds and preps the soil in one pass. A skilled tractor driver could do your yard in an hour. If they try to do it with a skid steer or bobcat it might take a full week, so the tractor is the only way to go. It will leave the surface of the soil loose enough to get those stones. Then you might be able to rig up a sieve to filter out the rocks from the soil. I would use 1/4-inch hardware cloth from a box store in a 2x4 framework.

Thank you for the reply. Please, be as blunt as possible. I won't get offended.

I live in Magna, UT. Just west of Salt Lake City,

The main reason I thought I had to do the tilling instead of having a big machine come in and do it is that there just isn't space to get a larger machine in my backyard. There is only about a 5ft gate and pathway from the front of my house that leads to my backyard. Other reason is that there is a slight downgrade in the yard towards my house that I need to level off to prevent any flooding, something that happened with previous owners.

I'm hoping to be done with weeds by Friday and begin trying to rake up rocks to see how much of a task or if raking is even viable to get it done. The more weeds I get up, the more unlikely it seems. Is it possible to rake out and remove as many rocks as possible then just bring in topsoil? Will grass root very well that way, or do the rocks interfere too much? I know I won't be able to get it completely cleared by hand.

Here are some pictures to get a better idea. Rock density size, soil a few inches down(basically just more rocks), and the only entry to my backyard.

Soil picture

Entry to yard

Round Up Plus Extended Control and a couple of other Round Up products DO contain a pre-emergent. As far as manure, even composted, it stinks for a couple of hours. I would never use straight manure or manure that is not "cured", if you will, due to the risk of too many pathogens still present.

As far as the rocks go, I had the same problem. We raked the larger pebbles up, picked up the actual rocks, and left the smaller ones.

I disagree about tilling. I tilled my yard to loosen rocks and remove them, then compacted it again, and raked the surface prior to seeding. Also raked the seed in a bit and re-seeded. As long as you re-compact the surface, you should be fine. Renting a compacter is much easier than stomping the dirt back by foot, and it leaves a much more even surface. That being said, if you have a small yard, a compacter may not be feasible and you may need to find other ways of compacting, if you are going to till.

You should get a soil test done prior to adding things like compost, though. You may not need the nutrients you are trying to add.