If I done a commerce/computer science (double degree) , how employable would that make me ; provided I take this route, what career pathways are open to me. I also plan to work overseas, maybe a couple of internships - so employability as a whole is a prime factor when I am researching courses.
At Monash? Depends where you want to go to. Monash is a great university and recruits well for most firms (with the exception of some of the very top ones like McKinsey, where they're treated similarly to Deakin, RMIT, etc).
Ultimately, a comm/sci double opens yourself to 99%+ of doors, the course doesn't matter nearly as much anymore as what you do within the course. If you want to work overseas, Melbourne has a stronger brand name to overseas employers (and thus will be better relatively, all things equal).
EC = extracurricular activities. Join club committees, start your own business, crush case competitions, etc