Well, I don't know if Christoph can dance. Not sure Goggins can either, but I'd bet on him - also because he's kind of wiry and lanky. Waltz has that Austrian rigidity nuance, naturally, a good fit for the Tin Man, I think Kurt might be a little old for it. I want the same actress playing both witches - two sides of the same coin type of thing. I would consider Margot for Dorothy but she would not be believable as a teenager. Maybe Brad as Floyd from True Romance being the Stoned Lion .
As far as screen time, it doesn't have to be a line-by-line copy of the original, this is the QT version. Sam can let the f-bombs fly.