What I did...
7 days in Kawaii at the Hyatt, really nice, very lush grounds.
7 days at the 4 Seasons in Muai, off the hook...saw Rodney Dangerfield walking all over the hotel with some hottie, for the whole week.
I prefer Kawaii, simply for the fact that it gets much more rain in the mountains, hence the lushness.
Maui has great resturants, I would suggest "Roys"
Do the drive to Hana, but do yourself a favor and go with a small tour.
Someone gave me a heads up about that, told me he rented a car and drove with his girl, and while its a beautifull ride up the mountains, past amazing waterfalls, it is a few hours, and when you get there, you'll probably eat, have a few beers, ect....then when you have to drive back, its pitch f**g black out...just you, the winding mountain road...and NO GUARD-RAIL.
I went in a small van with around 2 other couples, and it was insane...stopped at all these great private beaches, ate, drank all day, and slept on the drive home.
Have fun... and, "Mahalo" (say that, and you'll be good...stay away from "aloha" you'll sound like a geek.