I checked out Red Dwarf based on comments here. First episode was quite boring. Lister is a fuckup but he's not a likeable/funny fuckup. The whole premise is kind of retarded. A jr. tech who can't pass a basic exam is put in charge of repairing critical ship systems?
Rimmer was in charge of the first thing to go wrong in a chain reaction of fuck-ups.
Where has this ship been for 3 million years?
Holly set the ship on course out of the solar system in order to isolate the radiation contamination. Everybody was dead apart from one guy who was safe indefinitely, so no point in risking more lives.
Why are the catpeople perfectly fine if the radiation was deadly all that time?
They were in the hold, which Holly managed to seal from radiation in time.
If Holly can run the ship for 3 million years...
He wasn't running it, really. Once he had set the Dwarf to accelerate out of the Solar System, he read all of the world's literature, decided that the musical scale would benefit from two extra notes, briefly pondered creating the perfect robot companion, and quietly went computer senile. Everything else was on autopilot.
...why not put the entire crew in stasis...
The explosion took a few seconds to kill everybody on board except Lister and Frankenstein. Even if they had had time, there wouldn't have been enough booths, as by this point in time stasis booths were only used for penal reasons, interstellar travel having been abandoned after life wasn't found anywhere else in the universe. (Life would be found in later series, but the crew were several million years into deep space, where no man had been before, etc.)
until it reaches its destination?
There wasn't a destination. Holly was waiting for the radiation to reach a safe background level.
And here's that information again, in comic edit form!