Re: Torchwood in the U.S.
I think RTD actually had Martha pencilled in for Children of Earth, but filming schedules clashed with Law & Order: UK and he had to re-write (hence the Lois character). Wouldn't be at all surprised to see her back in series 4. Disappointed, but not surprised.
As for Mickey...not sure. Noel Clarke's been keeping himself pretty busy lately, but it wouldn't surprise me to see him back, either.