Re: Transfer Dragon Age Origins from Origin to Steam
The game cannot be transferred from Origin to Steam, only the other way around. Save files and characters are stored in a seperate location and should work in either version.
I don't know what to do about your missing files. The DLC is a simple fix though. The DLC should start downloading once you log into your EA account in-game. If not, you should be able to register all of your CD keys on the Bioware Social Network and DL them manually from there.