HIDs are a great mod, easy to fit, don't cost a lot, and make a *big* difference.
As for the ARBs, I've got the C-Ones and they're awesome. They come with bushes, whereas the Cuscos don't, so you might want to factor in the price of new bushes (in order to get the most from the new ARBs). The C-Ones also come with *much* stronger mounting brackets for the ARBs compared to OEM, again this should help you get the most out of them (with the Cuscos you'll be using the OEM brackets).
Something else on the ARBs, the drop links are notoriously hard to remove due to the way they're designed, and may actually need cutting off, which would mean you need new drop links (this is the same no matter which ARBs you're choosing). Something else to bear in mind as well.
A geo setup at WIM will be very worthwhile. Won't make any difference if you have this done before or after upgrading your ARBs, but as Aido said it will need doing again if you then lower the car.