I would take a lot of money and then give control to a close friend of mine
That sounds rather mean, if you know that he will probably be killed. That people will hunt him etc.
I would also do the same as skater_kid_who_pwns, because nobody should have world control. There will come no good from it. To much power make people reckless
Here is what I would do: travel to the past before I got world control and opt for a vast fortune and the power to manipulate people's thoughts and actions however I want to. Thus, I'll be able to make changes if needed, but I won't have the responsibility of taking care of an entire planet.
From who? Why the heck would you buy the Solar System when no one as far as humanity is concerned, has ownership over the other planets? Even if they "belong to us all", why would you need to buy them if you were already ruler of the world?
Then again, we could have aliens. Let's just assume that there aren't any aliens who secretly own Neptune.
If you're talking about exoplanets, you could go into the future.. Wait, even if you aren't hunting after exoplanets going into the future is a must. By then probably (maybe, just maybe) , we'll have interstellar travel.
what fun is world control? unlless you have have something to conquer it would be boring, so i would split the population of my world in half and apoint them a leader, and then that leader and his/her side tries to conquer my side, so last side standing wins. It will be and intense strategic mind game to command and conquer the world.