I just brought Oblivion 5th anniversy edition, now im reading that Oblivion and Shivering Isles have seperate patches.. but im confused on which I am to download, do I need both? or just 1? im desperate for an answer so I can play my new game.

I have no patch at all and the games work perfectly fine. They are not mandatory like in VtM:Bloodlines but they fix minor things here and there.

I have the 5th anniversery edition and it came updated to the latest official patches by default.
Have fun