Holy crap, you're alive!
As for costs, custom means expensive, last set I know of were well over $1000. In regards to the OBX, not sure exactly, the info is around, you just need to search for it.
To my knowledge no Australian company makes extractors for the 3VZ-FE or 1MZ-FE engines. You will have to get them custom made or import them. OBX in the US makes them, however I believe they require modifying.
No, do not do it. One very good reason is that your drive wheels are the same as your steering wheels. With all the weight over the rear, it is a recipe for disaster.
I have been using one of these for ages, 540CCA is more than enough. If you want a quality battery, you will have to pay for it.
http://www.supercheapauto.com.au/online-store/products/Century-Car-Battery-55D23L-540CCA.aspx?pid=287265#Cross
Hey man, hope you are doing well, I saw the accident pics on a mate's Facebook and heard what happened. Sucks to see one of the best condition JZXs in that condition. Hope the leg heals soon.