Well I say good on you if you go for it. It's an addictive hobby which could put you into some financial positions that you won't be used to.
However if I could offer some advice it would be this:
being a late starter as you will be, I would look to Companies that offer flight training but who also undertake commercial operations. You'll have a much better chance of employment after training if they know you and your strengths than the fresh CPL cold calling looking for work.
There's no doubt you will have to serve your time in GA (unless your father-in-law or any other family member owns a large scheduled service operation), so look around. I take it you are in Auckland if you are looking at the WIT/ Flight 2000 diploma. I am a staunch believer in getting out of the Auckland aviation scene unless you are already working in a ATO company.
I have posted before my thoughts on the "Pilot trap" that Ardmore and North Shore present. I'll go as far as to say that 90% of the CPL's trained at these airfields will spend a minimum 3-4 years post-CPL instructing, surviving on $10-20/hr flight pay
I would suggest that you look very hard at how you can accelerate yourself through your hours so that you will be an attractive employment prospect to B1900D, J41, SAAB 340 operators.
Just my thoughts
Cheers and good luck
S2K