re: Energy
I was think more along the lines of the Earth leaving craft try to match vectors as close as possible before making the link. Once linked, the incoming craft from Mars would act like a booster as both crafts started an orbit around the Earth. After the transfer of velocity, the crafts would separate. The incoming craft would decelerate into an orbit around the Earth while the outgoing craft is accelerated outwards towards Mars.
Something like this may never be possible, but it gets the mind thinking.