OK. Ill have a go but I probably the least qualified here to
1) My understanding is that if the build has comenced before this year, then it need only comply with the ADR on emmisions prior to what came in this year (79/03). Theres a few people in here part way through their builds that have been given a grace period in which to finsih their cars. Im not sure how to prove when the build commenced though.
2) My gut feel is that the jag is a better setup. I wouldnt discount the torana\commodore rear though, by the looks of things there quite a few cars our there with this setup.
3) Biased again, but the Ls1\ls2 is the best option. the 5.4 ford is allowed, but due to its size theres not many chassis that will fit it (unless you only need footwell room for one leg)
4) I thought Snake bite (Don Pilling) was a re-seller for harrison kits?? I could be wrong though. Ive only heard good things about Don, he makes a lot of quality Cobra bits at a good price.
5) ?????? I have no idea apart from the obvious things (quality of parts\build)
6) Most guys in NSW seem to use the same guy from Wyong on the central coast. Not sure of his name but Quite a few people in here should be able to put you onto him.
My best suggestion is that you spend a few hours reading through all the old threads in this forum. Lots of useful info, but always good in terms of the legalitites of getting car on the road to speak to the engineer.
Cheers.