OBSE install is a bit different for the Steam version, otherwise everything is is the same as for disc version. One thing to watch out for if you have Win 7 or Vista is that if you have Steam installed in Program Files folder, UAC may cause problems with mods.
Not sure about the save game, but i would quess that you cannot use it with the english version. I doubt trying would cause any problems though, the game will propably say the save is corrupt or from a diferent version of the game if it can't be used.