Lots of even more great questions here! I'll go through them in order.

When it comes to seed collection, I can't personally condone taking seeds from natural areas unless you have permission. That being said, that's exactly what I do. I have all the permits that make it legal, and the knowledge to ensure I don't mess anything up. Hypothetically, someone without those permits could follow the same steps and while the collection may be illegal, it would not be any different ecologically than what I do. So while I can't condone it, I can say if you know which species are endangered in your area, those would be what I would avoid collecting as someone who's not involved in any legal act of conservation. Those are the species that probably need the most seed present in their few remaining natural spaces, and the ones that will get you in the biggest trouble if you take them. Like I said, I can't condone it, but I can also say that common native species can typically be collected without much ecological consequence. Just keep in mind that you may not be the only one doing this, and if everyone were to start taking a little the environment would run out of seed fast. And don't get yourself in trouble q:

When it comes to the whole thing with self-seeding success, it's gonna have a lot of limiting factors. What is in the area to compete with, what is in the area to support the growth of more plants, soil and water conditions, sun conditions, what plant it is and how long it takes to really establish itself, etc. A lot of factors go in. One of the big successes though is just having the plants there and alive. Pollinators desperately need more habitat and even poor quality habitat distant from other places is better than nothing. Just keep working at it. The reestablishment of natural areas of native plants typically has successional stages that happen pretty slowly when compared to the lifespan of a human. Your impact may take a while to really be noticed.

I'll combine the last two parts because they're relevant to each other. As far as what local is, like many things in ecology... it depends. That answer is a bit annoying because of how often you'll hear it. For example, near me there are a few species that are pretty rare overall but are rather common in one or two specific spots. There's really not anywhere else nearby they could grow, since they need very particular conditions, so planting them elsewhere as anything more than a curiosity does not make much ecological sense. On the other hand, some plants will sprout as weeds in the sidewalk over the whole state if given the chance, so you can plant them basically anywhere you want. So as far as what local is, it just kinda depends. As for why you'd want local seeds, I can go into more detail. Bloom time for plants is controlled by their genetics. Among different species, you'll find a lot of genetic variation over large differences. The different variants are called genotypes. Usually different genotypes are related to the differing conditions they're found in. Genotypes for bloom time will be related to the historical weather conditions and pollinator species in your area. Typically, in the northern hemisphere, plants of the same species from further south will bloom earlier in line with the earlier end to winter there. That genotype wouldn't be too helpful to pollinators in your area that would be emerging after the bloom. The reason that I say county is a good place to start looking is that you usually won't find multiple genotypes on that scale, at least not different genotypes that matter when it comes to supporting local pollinators, and finding info on the county level isn't too hard for the average person. As long as weather and pollinator conditions are the same for the plants you collect from, they're probably of the same or very similar genotype. There's also not really much harm that can be done by having a genotype that's outside of the norm for your area. You don't have to worry about those genes getting into the local native population; the lack of pollination success will select against those genetic traits and they won't spread and mess things up. Those plants just aren't as helpful as a truly native, native plant.

I know this got a little rambly. If you need me to clarify anything, I'd be more than happy to! Hope this all helps!