If you want to do Engineering then I would strongly advise you do Specialist maths, I'm only in first year Aerospace engineering now (where the prerequisite was methods, English and a science), but I can tell you I would be struggling if I had not done specialist maths, or at least physics.
If you choose spec and chem, but don't do physics then you will find uni physics way way easier to pick up, than if you had not done spec. But VCE chem (From what I have heard) is harder and has more work load than VCE Physics - something to consider. Most engineering, however, is much more math/physics orientated than chem/maths (Unless you do chemical engineering - but you still need to be strong in physics), but VCE Physics is pretty lame and VCE Chem is pretty good (to be concise about it).
As for commerce, don't quote me on what I'm about to tell you, but from what I have heard from friends, doing anything in VCE related to commerce or business degrees - such as Accounting or bus man - it is pretty much a waste of time. Only in the sense that nearly all of the stuff in the VCE course is entirely covered in uni anyway and thus you could have done a subject which would be more beneficial such as spec or physics.
Further will be of no use to your degree, it will boar the shit out of you (in 99% of people who respect maths in some manor anyway), and..yeah don't do it

In summary I would recommend doing either one of the following options:
1 - Spec, English, Methods, Chem and Accounting
2 - Spec, English, Methods, Physics and Accounting, or if what I said about accounting was true and you feel confident in your study ethic;
3 - Spec, English, Methods, Chem and Physics.
That's what I think would be most beneficial to you given what you want to study, but if you think that would be to much work then perhaps consider:
5 - Further, English, Methods, Chem and Accounting (If you want to do Chem Engineering)
6 - Further, English, Methods, Physics and Accounting