you cannot but you can become a blade
You never become an actual god in Oblivion.
no
No, you are not a dragon in Oblivion, nor can you become one. You might be thinking of Divinity 2: Ego Draconis.
you cant in oblivion without a mod
no
you need to download a mod in order to do that. you can only download mods for Oblivion if it is on your PC
finish all the deidric shrine missions
yes but you have to buy a spell from a spell trader
When your conjuration skill reaches level 50.
Search for a Mod called Kvatch Rebuild or Kvatch Aftermatch.
Go to the arena in Imperial City, and defeat all challengers.
I blew them to oblivion with an atomic bomb; they were blown to oblivion; the Universe was sucked to oblivion; its like they appeared out of oblivion