Why do you even have Rinne to begin with? If I was going to grab a third goalie that was a backup, it would be Ty Conklin, Halak, or Harding. Those three at least have solid defensive teams playing in front of them.. and Conklin will get every 3rd/4th start or something like that to make sure Osgood is good to go in the playoffs.
Trading Cam Ward might not be a bad idea, but if I were to trade him, it would be to "upgrade" and try to grab a goalie that hasn't started very well but is a well known stud.. Luongo and Turco come to mind there. Either that or trade for a goalie that will put up similar numbers by the end of the season and try to get a skater out of it that way. From the sound of it, you wanted to just run with Miller and a backup on an average Nashville team which probably isn't the best idea. Ellis is going to get most of the starts. Though he'll have a good year probably, Miller's stats will turn a bit more human (sorry DM) and running with a single starter goalie will be a struggle to take the wins category each week.
I don't know what your skaters look like but yes trading Cam Ward is a good idea based on his numbers. I'd try to get Luongo or even Giguere for him, though. Then you can dump Rinne and add a skater from free agents that way.