Don't know about the erigeron, but the allium and eryngium are fairly simple. sow onto moist compost, cover with fine compost so they are just covered, label...............
The Eryngiums will germinate fairly quickly, the alliums may take some time to show they are doing sommat.
As a pointer, only sow a few Eryngiums, about 5 in a 3" pot and about 10 in a tray.
Handle with care as the blighters bite back. And don't plant out many. Once the Eryngiums get established they will grow into a sizeable clump. one plant could become a 3' sq clump in a couple of years, and not one to tackle light handedly.:-)

Hi again. Once again, thank you very much for your invaluable help. I'm really looking forward to sowing all my seeds and raising some plants for my new garden.:-)