short answer - about 18k for an auto or 20 for a manual.
long answer - at 100k, most cars, and especially jap turbos require a timing belt change. this is a glaring omission from his details. this can cost upwards of 1k, so be mighty careful.
you probably also want to find out how far back the exhaust goes - i.e. cat back or turbo back. this isnt a big deal, as the cost of fitting it later will be small, but it does give you an indication of what the power output SHOULD be.
Bilstein shocks = coil overs or single shocks?
what brand are the mags? aus or japanese? what state is the kit in, cracks etc.
these are all things which you need to ask them and yourself.
you may also wish to get a leak down test done - a lot of people here have used them as an indicator for what sort of life the engine has had.
finally, be aware that the aussie dollar is VERY strong against the yen at the moment. private importing is a personal question, but it may be worth asking whether waiting for 3 months is worth the (up to) $3,000 that you might save.
I bought my car for $20, on the road a year a go. I could probably buy the same car now for $18 even though the import scheme is now more expensive..
and YES, the drive will sell you. welome to SAUWA.