May as well spend the extra and get the VXR over the regular SRi Turbo. The Z20LEH in the VXR has a few extra little tweaks, like oil squirters under the pistons to help keep them cool.
As for rego in WA, contact your local authority for more details. Trust me, it's not that hard to make a phone call and ask. If it's anything like SA though, any car from interstate pretty much just needs a Tier 2 identity check, which is roll up to the inspection station, get them to check engine numbers, VIN, etc. and pray that it ain't stolen. After that, it's roll around to the rego office, register the car and get your new plates.