Dwatson, we do "prairie plantings" around stormwater ponds and I've got a good handle on the procedure. Let me just state-we use cover crops as a regular part of our seedings but for a different reason than the one you propose: Simply put, some of the cover crop species get up and get growing very quickly. This then helps to hold the soil and reduce erosion while you're waiting for the meadow plants to get growing. so I would say yes, but for that reason, not the one you offered-that of competing with weeds. Keep in mind, any cover crop planted will also compete with your prairie/ meadow species, so weigh that carefully. You don't have a big area here nor do I see much slope. As such, you may be able to forgo the cover crop completely. Either way, the weeds are going to come. Your judiciously timed mowing will help there, as will the growth and development of your seeded in stuff.

Based on the picture you posted for the effect you are after and the question of which to do first, I'd start with the cottage look first and then secondarily sow seed to ease in the meadow as filler. After that, trial and error on which varieties from the packet you like as opposed to other types not so much, you can edit or save seeds for next year to have more plants where you want them and let it evolve in a way that you like. You will want some definition and structure since its an urban backyard so purchasing some woody perennials and ornamental native grasses will provide that and give structure & definition in the spring and during the off season, rather than one big blank slate. You can select plants that will form some mass and place them in a pleasing way.

I looked up the seed mix you ordered. Except for the Little Bluestem, the grasses are a bit coarse in that mix & not the most decorative native grasses to choose from so I don't know how you will like them once they reach maturity. Common yarrow can seed like a bandit in good conditions and so can Lanceleaf coreopsis, you sometimes end up with some plants simply taking over at the expense of less aggressive ones in a garden situation. I ended up culling certain overly aggressive types out. They are good for starting due to the fact that they are easy to grow but sometimes they are too competitive. Its trial and error.

I've done the same thing here and found its easier and more successful to select individual seed types to plant where I want specific plants, I sow directly or start them in pots to set in where I want them to grow. I didn't like the results of just tossing a mixed bag of seed and waiting to see what happened, a mess is what happens sometimes and nothing in gardening is usually that easy. Its one thing to sow that way on an acreage, quite another in an urban yard.

As far as weeding is concerned, I hand weed mine. Its not as bad as you think and once you get it under control, its a matter of maintenance and discovering what plants have naturalized, which ones you don't wish to keep and ones that petered out or somehow just didn't work out. Another downside about the idea of just sowing mixed seed and hoping to get a nice looking result is, you can't tell the good from the bad when they start coming up along with the weeds.

Just one more note. It is recommended that you clear the area of all weed seed prior to sowing. You can use various methods like covering it in plastic for a time until the plants that germinate cook or eliminating all weeds that come up manually until the area is clear or using a product like Roundup to eliminate them. Any time you till an area and it looks like that is what you did, you bring up new seeds so you will be dealing with weeds for a time. Its sometimes easier to Roundup an area and not dig at all. You then sow the seed once the area is cleared.

I've never quite understood the concept of mowing to control the weeds because you mow everything when you do that so I cannot understand how the good guys will end up taking over while the bad guys will magically disappear. All I can see is you might prevent seeding but mowing seems like the wrong way to go in a situation like this, it might make some sense for weed control in a lawn but not a meadow and even at that, it doesn't eliminate weeds from a lawn, in fact some prairie grasses will die if mowed more than a couple times per season.

Tex, on that mowing, it helps with biennial stuff like Queen Anne's Lace-cut it early in bloom and it's done for-as well as tall agressives like sweet clover, where there's just no good option. IF you can at least do that, you knock back one seed cycle, while presumably, your slower-to-establish warm-season grasses kick in. If could be too that that matters more here, where cool-season stuff is always ready to pounce, not sure about that. But we usually do one or two high mowings in a new prairie establishment, and it seems to help. The general feeling is that the real early stuff like Rudbeckias will bounce back anyway and I find it to be true most years-they have time to flower and set seed after getting mowed back.

So very different to creating an English wildflower meadow where soil impoverishment is absolutely key...so much so that we routinely remove topsoil and add parasitic plants such as yellow rattle to predate on the grasses. Also, we would take 2 full seasons of complete weed removal and continual hand weeding for several more seasons. Finally, a common strategy is to lay in a sand mulch on top of the base soil and sow seeds directly into that (although we may well add in plug plants throughout the season. And yes, mowing plays an important role here - we would always do a late mow after most of the flowers have been able to set seed, then continue mowing until mid autumn, then stop until the following year.