Hi Satyams,
Choice of Vic or WA is for you to decide. If you feel the job market is good for your occupation in WA, then go ahead with your 176 using the SS approval in hand, but if you feel Vic is better then I would say give it a week or two to see what the result of your application is to apply for 176.
CO gets allocated within 4 week's time for a 176 application. So if you plan to wait then make sure you have all the docs ready like the PCC & other employment reference letters. You can easily do the maths to make sure you dont step into July to avoid impact of any sorts on your application & are granted the visa by June itself.
And to answer your last question. NO, it is not possible to transfer your SS once you have applied for the visa.
Btw, whats your skill code?