I changed my mind and decided that I like "Ten years after Palpatine's rise to power in the Galactic Senate," best since it links what the state of the galaxy was before Palpatine took over and what it's like now better than "rose to power" does.
I am going to state my case as to why certain elements would make a bit more sense or sound better one way or the other. So, here we go.
Assumed Leadership of
Gained Power Over
Rose to power
Rise to power
Like I said before, I think "rise" gives a you a better sense of the what the past was like. I also like it better than "gained power over" since the phrase seems a little weak dramatically. I think "rise to power" has a more sinister tone to it which is fitting when talking about Palpatine. Oh, and "assumed leadership of" is too straight forward; no undertone of evil at all.
This final paragraph is what you asked for.
I think the spacing issue won't be an issue anymore. Whatever elements you decide to go with I should be able to make work.