here is a view of a non-Newzealander, who likes the country and people a lot:
For me the Kepler-Track is not very impressive. Possibly because it leads through a landscape we also have here in Austria.
I had the impression, they created it to relieve some stress from the Milford track.
The Milford track is impressive, but rather crowded, but maybe in March it's already easier, I don't know. Normally you have to book it for months in advance to get a slot. Unfortunately the sandflies don't need to book it, they are just there.
As John already mentioned, the Tongariro northern circuit is fantastic, we liked the volcanic landscape, and I can really recommend it.
We also liked the Abel Tasman track very much, but we have been there at begin of december, when it was not so crowded.
Possibly for a Californian a coast track like that is not so interesting, I don't know, but we enjoyed it a lot.
For the above mentioned Copland track bring an ice axe and crampons, and don't do it alone. If you really have only one week, I wouldn't do it, because of several reasons.
The west coast glaciers didn't impress me much, possibly also because glaciers are a common thing in Austria, but mainly because of the tourist crowds and the business around them.
The southern part of the west coast is a very lonesome area, especially if you leave the Doubtful sound behind. But to really enjoy it, you would also need more than a week time.
We also liked the area around Wanaka, there are great short hikes, and the lake is fantastic and also the view to Mount Aspiring (e.g. from Mount Roy, which is an easy day hike).
Wanaka is not so crowded like Queenstown, which is also a nice place, but to many "rubbing shoulders".
If you drive towards the Milford sound from Queenstown, there are some really nice day- or 2-day-hikes on the way, which are not so well known and therefore less crowded. Just buy a good map and look into it, and explore valleys without tracks or trails.
But now I must come to an end, otherwise I cancel my job immediately, buy a ticket and spend another 3 months in this nice country.