8000 miles
The most populated island in the Pacific is most likely Australia. Although some may argue that it is really a continent, it does satisfy the definition of an island. If you were asking about the most densly populated island in the Pacific, it would have to be Japan.
If you start in San Juan and drive around by the coastal cities, it takes very close to 6 hours according to Yahoo maps to drive around the island of Puerto Rico.
Around 8 hours.
Just to drive? Definitely, but probably not long enough for a good look around.
The flight would be around 8 hours.
According to Google Maps, it takes about 1 day and 13 hours (2,219 miles) to drive from Long Island to Utah.
Almost the entire day with minimal stops.
Distance between oahu to kauai is roughly 100 nautical miles. Assuming the wind is good, steady and from norhwest, you can make it in about 6-7 hours, give or take one according to the conditions.
There is no direct flight, so it depends on the number of stops. If only one stop you are looking at around 8-10 hours.
17 hours to drive from Toronto to prince edward island
13 hours