sucks to hear :S I know how it feels, been done twice now.
How long did they give u to drive it? I think i got 40 hours or something like that.
Regarding rego - There are special cirumstances that allow you to re-register while defected, I did it. I went to the rego place at regency pak (next to where u get defects off) and paid the normal rego, and they gave me a temporary rego sticker that gets put on your window- its paper and bigger than normal rego. Then i went to cop shop to get my clearance to drive (once all the 'defects' were fixed). That way you can still drive around until your regency date.
So try do that, fix the defects.. get to regency motor reg and pay rego to get your temp rego sticker, then you can drive around still, get to work etc without any worries.
Id put stock rims back on, just for caution, and maybe go see AAA exhaust (at west richmond) to get them to fix your exhaust, they helped me out heaps for about $70 i had stock exhaust put on for the day and then old exhaust replaced after. They may charge more now but theyre pretty helpfull when it comes to defects, they helped me with both my defected cars.
Hope thats some help