Both. It's targeted by injecting into one tumour, but many different tumours can be targetted. Once targetted, this tumour is eliminated along with all "copies" in body. If you had breast cancer and colon cancer you would need two injections.
Yes, but it's hard to say yet how much different the therapy process might be in humans. The treatment regimen could differ from mice significantly. (Human tumors may be buried a lot farther away from the surface than in a mouse, and thus, harder to dose accurately with a long needle.)
It's also not clear what toxicities were incurred with this therapy (in mice), which is a significant concern for the approval of any drug in humans.