1) a space probe sent microscopic records back of every lifeform (took 5 months to get the signal), as well as chemical tests of a huge number of them for toxins, but found few toxins that could hurt humans (ex: a type of lichen that can survive much higher levels of arsenic than humans is fatal if eaten due to arsenic buildup in it). They haven't tested viruses or the like, but it's unlikely their micro-cellular life could effect humans or Earth life.
2) Spectroscopic analysis shows no refined metals, except on the hot side where it happens naturally. There is also no sign of artificial electronic activity, though if it was far underground it would be shielded from detection.
3) The trip is one way, due to fuel, though only LH2 is needed as fuel, so it can easily be made two way. Takeoff is done by heading north or south until you clear the canyon wall, then heading over the hot side to get the extra lift from the heat coming off of the ground. The 747-8f has 855 cubic meters of cargo space, so let's say ours has a bit less (as some will be taken by the reactor, crew space, etc.), say 825 cubic meters. They need two cockpit crew, though I'd guess a spacecraft would need at least 4, say a pilot, engineer, doctor, and another. The 747-8i can seat 605 passengers, so I doubt you can fill up on passengers.

It took 17 months to get there, so any trip will probably be one way anyway.

Questions are great. I like someone who knows details about what they are doing.
[url=http://en.wikipedia.org/wiki/Boeing_747-8#Cargo_aircraft]747-8 info[/url]