Judging solely from the beta, the story does seem like it will fly by quickly. However, I found myself not even caring about its briefness and enjoyed it anyway. IMO, even if the story is short, I don't think it'll be a problem. There's also a lot of replay value in them. (On a side note though, I think I read somewhere that there will be a significant amount of story missions.) In regards to the number of planets though, I'm pretty sure its just going be the ones we saw announced when it launches, but there's always the possibility of more being added in later, which I'm sure they'll consider. There's too much potential there not to. One thing I'm half-hoping they'll add though is ship battles. But I doubt they'll do it.