My wife & I just returned from our 5th trip to Kauai in 7 years. We always stay for 7 full days and I think 8 would be better. Lots to see and do on that island.
As to where to stay, the south shore (better weather in November) has the resorts and expensive, but nice, touristy restaurants. However, we are not among the beautiful people so we stay in a condo on the north shore (much more beautiful but not as touristy). Try these links for a condo on the north shore:
Condo Bob's Princeville Kauai Vacation Rentals We stayed at the Sandpiper, #229 and it was georgeous!!! All for $100.
Brewers - Kauai - Princeville Vacation Rentals We have stayed in one of their places a few times and were very pleased.
Here is a link to the single best Kauai guide book on the planet. I urge you to get one of these!! They cost about $16. We agree 100% with everything they say and they live on Kauai.
Wizard Publications, Inc. / Believable Guides for Unbelievable Vacations
HAVE FUN!!