So now the question is just size?

That is pretty tough to answer without getting into specifics (how big is too big? do you need all the data you are including? etc)

You could look at working in ROLAP mode instead of MOLAP, which would save space in the cube, but make things slower (and increase space usage someone in the dw). Other than that, your only method I know of is getting rid of things you don't need.