Nothing really wrong with your film choice, though Velvia 100 has a tendency to blow the whites more readily than, say, Velvia 50, which will do so gracefully. I have also not found the reds particularly welcoming when and where I have used polarisation (rainforests, for example), ditto impetuous Velvia 100F, often worse in this regard. Places like The Caitlans have a few exquisite waterfalls within good walking distance, but also terrible rain and biting cold. Lighting down there can be very poor, almost dark in the middle of the day, so having some higher speed, lower contrast film like Provia 100 is wise to hedge against reciprocity. Take a polariser to enhance the depth of greens and the reflections, especially at Lake Mathieson very early in the morning with the Southern Alps looming high above. Lots and lots of blue light in shade and at higher levels, so the warming filters are useful, but I would still angle for the pol to bring up the punch.
At this time of the year I'd be focusing (sorry...) intensively on keeping warm and dry as far as possible. It's a hard task to master carrying gear! And such a striking contrast to e.g. Haast Pass environment which was cold but not as wet. Not the norm, but the exception.
Beware that NZ Customs outbound can be very touchy-feely with cameras and will no doubt pull you aside to examine your gear very inquisitively. They'll also question you if you have a lot of stuff and want to make sure it hasn't been stolen. In the early 2000s (2003-2006) there was a stolen camera equipment racket festering between NZ and Australia. Customs eventually nabbed the culprits in Auckland, but a lot of expensive stuff slipped through and was sold off on the black market, or eBay.
I've finally got back the 6x17cm home made pano built by SMBooth in the last couple of months of 2010, now in its Mark III form after a focus correction. I'd take it to NZ too (along with a truckload of other cameras...)
Find your wings and enjoy. Dont' forget to send a postcard!