The events leading up to the phantom menace are covered in the novel cloak of deception.

Palpatines plot to became Chancellor. Pretending to be friends with Chancellor valorum engineers the trade dispute and the nemodians blockade of his own planet.

While playing the duel role of Palpatine and Sidious. Which i knew about already though i think the novel tries to make you think they are 2 separate characters.

Basically the sith Plotted for a thousand years from the shadows for their revenge. Palpatine could conceivably due to dark side techiques be hundreds of years old.

He says in Revenge of the Sith that he waited a long time for this.

I think he wanted a thousand year reign of the sith Through the Empire. How many years did it last no more than decades, not even thirty years.