There is a LOT of groundwork you need to do before you could possibly have your own government. Moreover than a planet, you will in fact need to control your own SECTOR. Now, you might be able to find someone willing to sell you a planet, once you've earned enough money to pay the going price for them, but taking control of a sector is going to take a LOT more work, and probably either some incredible diplomacy, or making best friends with an existing government leader who has multiple sectors and decides to let you have one.
I'm not suggesting you abandon your goal, but I highly suggest you set yourself some lower, simpler, interim goals towards reaching it.
____________"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."
Only fools and children dream of heroes.