So it has already traveled 2.3 billion miles and then will return to Earth having traveled 4.6 billion miles? I know, the return trip may well be significantly shorter (or longer) but for a round trip endeavor, that has to blow away all previous records. Does anyone know what the previous record is? One of the Apollo missions, maybe. Did we ever bring anything back from Mars or Venus orbit?
Yes this would qulify for the longest round trip mission, although there may be some questions on that since the craft dosen't actually land, just a released capsule.
There are plans in the works for a sample return mission from Mars in the next 10 to 15 years.
No mission has ever returned anything outside of lunar orbit.
Venus would be verry difficult for anything but upper atmosphere. Probes don't last above a few minutes with pressures 10 to 50 times that of earth, tempatures on the surface aloow for molten rock on much of the surface and sulpheric acid for rain.