Not a present, but there are certainly creative ways you could do something similar with the current perspective.

Will "power-ups" or "weapons" ever be added?

In our opinion, the spirit of LittleBigPlanet was to "figure ways around obstacles" and less about blowing stuff up, though certainly a player can already create their own experience to include missile launchers and the like.

When will users be able to "sell" their creations for real money, ?

There are still a lot of details that need to be worked out, that's pretty much all I can say at this point.