Indeed, it does seem to be one of the MANY species of Goldenrod. The only problem is that this genus hybridises so very easily that even skilled taxonomist have great difficulty in identification. As for the seeds: haven't your parents ever told You about the birds and bees? Flowers are reproductive structures and consequently produce seeds. Wait until the flowers begin to show white fluff, cut the entire inflorescence, store it in a paperbag for several weeks, then shake out the small seeds.I might add that Goldenrod seeds have a low rate of germination. Good Luck!!!