Seeds or Plants

Every gardener is confronted with the same question - Do I start my landscape with seeds or with established plants in pots? It is a very legitimate question and it has bearing on a number of very important future results. Both approaches have merit and both have limitations. I've been gardening all my life it would seem - at least since I was able to toddle about, and I've used both with great success at times. It just depends on the setting and the goals you've set for your landscape.
Seeds can be a very economical approach if you are limited in budget; if - and that is the operative word - you can find a reliable seed source for the plant species you wish to add. You can often purchase a relatively large number of them at a reasonable cost. Every week (daily at times) I see posts to social media of people looking for seed to start their wildflower garden. I understand and sympathize with their desire, however, it is often poorly directed. Starting a landscape planting with seed has several limitations. For one, simply scattering seed on prepared ground rarely produces more than a handful of plants that will reach maturity. So many things can prevent seed from becoming established plants. Seed viability (its inherent ability to germinate) varies greatly by species. Some remains viable for a year or more. Many others decline precipitously 3-4 months after maturity. Here in Florida, most of the Asteraceae that I routinely work with - blazing stars (Liatris spp, for example) will rarely sprout after 3 months. I find that I have to sow them almost immediately after they are ripe. This isn't as big a problem in more northern states with cold winters, but even then seed does not remain viable indefinitely. If you choose to use seed, make sure it was collected as recently as possible. "Good deals" on older seed are not good deals.
Second, seedlings are like infants. They are vulnerable to vagaries of weather and herbivores after they sprout. Many that sprout do not make it to their juvenile stage where they are reasonably well established and able to cope better. They need to remain well watered and pampered after they sprout.
Third, an open-soil garden where seeds have been scattered is the greatest welcome mat possible for weeds to also establish. It is not possible to create a wildflower meadow without a firm commitment to weed everything that isn't supposed to be there aggressively. Without that, you will end up with a weed patch instead of a wildflower garden and the weeds, over time, will do their best to crowd out the few real wildflowers that have emerged.
Using established plants is a sure way to bypass having to pamper a bed of seed and young seedlings. It is expensive, however. Most 4"-sized wildflowers will cost $3-5 a piece. Planting any-sized beds this way can cost hundreds of dollars and that is beyond the budget of many of us.
Over the years, I have adopted a compromise. I use seed for a few wildflowers that I know to be extra rugged and I purchase plants for the others, collect their seed over the next few years and grow them in flats. A few I leave to self sow when I know them to do that reliably. By collecting the seed of my own plants and sowing it in flats of potting soil, I can produce dozens more, pot them up until they are large enough to establish themselves in my landscape, and then plant them exactly where I want them.
I started my hobby wildflower nursery, Hawthorn Hill, because too few of the wildflowers I wanted to use were available in the trade. I had to grow my own and I often ended up with more seedlings than I needed. To date, I have added more than 2 dozen wildflower species to my landscape. Some of them were originally purchased plants, but all of them are seedlings that I've grown from seed - just not seed scattered across the soil in my garden. I propagated them from the seed of plants I formerly had in my former Seminole landscape.
I've got at least a dozen to two dozen more species to add. I'm just waiting for my seedlings to get large enough to transplant. My wildflower meadow is purposely planted. It is not a hodgepodge of whatever comes out of my soil nor is it serendipitously arranged. I'll add the taller plants to the back and the shorter ones to the front. I'll plant the ones that need a slightly moister soil in the slightly shadier and lower parts of the spot I've chosen to garden in. Over time, some will expand on their own and I can then decide to leave them alone or to weed them out where they are not wanted.
To be truly successful, a wildflower planting needs to be managed unless you have acres to work with. In my small 18 x 9 ' plot, I have to be careful about what I add and where it gets added. By doing so, I can maximize its diversity and, hence, its value to the pollinators I'm hoping to provide for.  I cannot simply scatter seed and I most definitely cannot simply wait for whatever emerges and then weed out the non-natives. That approach is always bound to fall far short of its overall potential no matter where you garden. Target your garden with a purposeful palette of plants. Often, that means that you will have to purchase some to start and then have the patience to either propagate them yourself or let them self sow over the following years.
There is no "quick" way to reach your full potential. It takes time, patience and a little forethought.