I use rubbing alcohol in a spray bottle and I spray the aphids directly. It kills them and evaporates without leaving any poisonous residue. I usually have to go back a time or two before all of the aphids are gone, but it works great. It's a hardy weed, so you don't have to be too careful. Put it where it will get some moisture.
Full sun is fine, but it does well anywhere.
That will depend on the climate where you are. I live in Southwest Florida and they are in my yard and laying all year long. If any of you Northern folks would like to tell me about your areas, I'll post the info here. Most of mine have survived for years and years, except a few that didn't make it through our droughts here. I'm not sure, but I get the impression that they don't.