Yes, 5x4.500 is equal to 5x114.3, which is a common PCD. Nissan, Honda, etc. all use this bolt pattern as well, but with different centerbores.
I would say 67.1mm is most likely the measurement of the actual wheel/spacer bore, as there needs to be a certain amount of space between the actual hub of the car and the bore of the wheel to eliminate binding when installing or removing the wheels.
I would only run spacers sourced from a reputable company, you really don't want to have issues with your wheels!
And yes, threads are 12x1.5.
When I actually get my car (should be Saturday!) and I get it on springs (H&R or Eibach if they finally figure out the euro 6 is the same as the US 6) I'm going to be doing a bunch of measurements to figure out the optimum ET for running a set of 20x9's with 245/35-R20's. Right now I'm leaning toward +35mm, but we'll see!