I have read in the past that weeds that have died and shriveled up have a completely different composition (is that the right word?) to weeds that have been picked and then dried, which is why I wouldn't feed dried weeds.
As for growing weeds from seeds, it's easy, what's wrong with you people!!!! Don't try to grow them in seed trays, all you will get is tiny weedy things that then die. Only grass will grow like that. You need either a really deep tub, or a part of your garden that you don't use. If using a deep tub wet the soil, sprinkle the seeds on and cover with glass, or even clingfilm. Then leave them alone until the weeds are a couple of inches in height... You might need to water slightly once they germinate, especially if the weather is hot. If you are using the garden make sure the soil is damp and then just throw the seeds on and leave well alone!! I have found if you throw the seeds down in autumn, you have some lovely seeds germinating in the spring

. You should see the size of some of the dandies and thistles I have in my weed patch..... I think the dandies will soon be bigger than TT's and Terry's.... I shall have to get photos!!
I think you are all expecting your weeds to germinate and be big enough for your torts in a couple of weeks.... That won't happen! If you sow them under glass they will germinate quicker, but it won't happen over night!