Grass seed is pretty tiny. The rule of thumb is covering that seed no more than 2-3X its widest diameter. If you put 1/2 of top soil on your seed it will damp off, rot and never germinate because it was buried too deeply. Or shaded. (This is weed control).
We need to see a picture or two or three of what you have going on...reseeding is ONE way to take care of bare spots in your lawn. What is far far more important is that we solve the reasons for those bare spots. If you are thinking over seeding will make your lawn more lush and thick, think again.
Quit reading sites done by Ortho or Scott's like right now. Ugh. They WANT you to fail so you keep buying products to fix what happened because of their stupid information.
I can tell you I am an EXPERT with this cool season grass MONSTER called a lawn. I learned what Ortho and Scott's would not tell you nor do they even know themselves. The only PRODUCT that is necessary to add 3 to 4 times per season is fertilizer. The FAST greening stuff from Scott's or Ortho that ishigh high high in nitrogen is not healthy for lawns. Too much too fast, causes stress. The slow release, ugh ORGANIC, type fertilizer is worth its weight in gold. I hate using the word organic, or natural...so misconstrued. Go get Dr. Earth's Lawn Fertilizer and try that for the next application. Costs more, lasts longer and also comes with bacteria and fungus...one bacteria EATS thatch...decomposes thatch. But please bag your clippings.
Mowing close to the ground is called scalping, for a good reason. It weakens your grasses and can also damage the crowns of clumping grasses. For overseeding, makes sense, you don't want to shade out your grass seeds.
Otherwise, keeping your lawn NO SHORTER than 3", 3 1/2" is best...is top of the list for a lush, drought tolerant, crops with no or few weeds. No shorter. Not ever 1/4 inch shorter. Talk about that later.
But we need to back the truck up! Why are you overseeding? Have you tested the pH of your lawn's seed bed? What do you do for maintenance? Mowing height, watering skills, aeration? Fertilizer? How do you mow, and how often do you mow, sharpen your blades? Do you aerate by pulling plugs once per year? On lawns in your past? Have you ever had a maintenance company involved? Do you have an automatic irrigation system for this new home?
Bare spots mean there is a big problem we need to solve first. How much shade do you have? Where do you live? Do you even have cool season grasses (I am assuming because you are overseeding)? Milorganic 'fertilizer' is not a balanced fertilizer. All fertilizers need to be spread with your hand spreader (by Scott's, grin)? No hand drizzling allowed! You should also rent a water filled roller and go over your entire lawn before the seed starts germinating. Ensures better soil/seed contact. For these next two weeks you will have to water shallowly and often. Do not allow the soil to dry out. This is the only time you get to water your lawn shallowly to keep the top 1/2 inch of soil moist, NOT SOGGY. Might take 2 or 3 or more times a day if the weather gets warm or windy. No more fertilizer for awhile, okay?
More information please and please check out our stuff on seeding/sodding new lawns and how to take care of cool season grass crops called lawns...
Correct maintenance and knowledge of your 'crop' of grasses will enable you to use the least amount of work and water. We've got lots of other Question/Answers about this BEAST. Go look them up. Far better than Scott's telling you how to grow a lawn! Grins.