There is only one species of ash that grows in the NW, so you've probably been using Oregon ash. There is also mountain ash, which is a completely unrelated shrub that grows as higher elevations. If you're in Eugene, then you're in the epicenter of Oregon ash's range. It forms entire forests (small ones) along Coyote and Spencer Creeks as well as at Amazon Park. In the West Eugene Wetlands you can often see it resprouting. It grows very easily both by seed or from live wood. I've never tried transplanting it, but in the forest it resprouts very easily, so I'd imagine its easy to move. Its a wetland tree and 99.5% of our Willamette Valley wetlands have been converted to agriculture - mostly grass seed farms. So I think Oregon ash has been drastically reduced in its extent. Its also a very important habitat tree for birds, insects, and lichens, and supports (along with wetland oaks) the best NW foraging spots I've ever seen. So I very much believe in finding spots to grow it and its associated plants.
As far as the nettles, you can certainly spread them via seed. You can also transplant rhizomes (the roots that grow laterally from the base of the plant. You'd likely want to do either in fall. Maybe October/November. Prepare a spot by clearing invasive species, then put down a mulch, plant rhizomes and sprinkle seeds. That's about all there is to it. Nettles are an aggressive plant that can hold there own. But they do need moist, yet well-drained soils with lots of organic matter. So finding the right spot is important. Other plants are similar, though with varying degrees of pickiness. Every species has a type of soil and a shade/light regime that they prefer. Most plants also can be spread either by a part of the plant or by seed. Its just a matter of getting comfortable enough to experiment. Nettles and thimbleberries are good ones to start with if your in a forested setting. Valley bottom, camas isn't a bad option, though I'd recommend seeding camas unless you can salvage the bulbs from a spot that's slated for development.