Swiss pass or half fare card

I've done some research on what options to take, but I just need some advice on what is the best option for transportation to be travelling within Switzerland for 5 days 4 nights. This is our itinerary:

12/17/2012 Arriving in Zurich from London at around 9:30am -> staying in Interlaken overnight
12/18/2012 Find a good package for visiting Jungfrau/Grindelwald, etc
12/19/2012 Interlaken to Zermatt (staying in Zermatt overnight)
12/20/2012 Zermatt to Geneva early morning
12/21/2012 Geneva to Paris (take tgv)

Questions:
1) Should we choose swiss pass or the half fare travelcard for our travels (including TGV on last day) within Switzerland?
2) Is it cheaper to get a package deal to visit Jungfrau like the link I've attached below or is it cheaper to decide along the way?
http://shop.jungfrau.ch/en/bergbahn/angebote/jungfraujoch-top-of-europe/jungfraujoch-ticket-anschlussticket-zum-ga-und-swisspass-ab-wengen-bis-grindelwald
3) Does the swiss pass include the fare up to Zermatt? or 50% off?
4) If I get the Swiss pass for 4 days (12/17-12/20), the the TGV on 12/21 would be purchased separately. Does half fare travelcard have the 50% discount on TGV as well?

Thanks so much!