1. if Darth Vader could destroy a planet then I think that palpatine should be able too since he's as strong - or maybe even stronger - in the force than Vader is. need i remind you of his lightning sparks (or whatever they are).

2. nobody really knows what the force can do, that's what makes it so appealing to SW fans and that's also why the midi chlorian explanation is generally disliked (since it lessens that mystery).
it follows that we also don't know what the force can't do, I think that find the base and the stolen data and destroy an entire planet are part of it.

3. thanks for the quote correction DJ but I'm too lazy to go and change it...