Island hopping is super easy, I walked right through the Hawaiian airports with no problem. Maui is very nice, there's lots of good snorkeling there. You can fly into anywhere, just go wherever is cheapest and see that island first then hop around. I'd make sure you hit Kauai as it's the least touristy of the bunch. Very third-world, but still America if you know what I mean. They've shot about a bazillion movies in Kauai so if that's your thing go you can drive to all the spots.
On Maui I'd skip the "road to Hana" as it is literally HOURS of super twisty, edge-of-the-cliff, sometimes one-lane roads with rock-slides, gravel, idiot tourists, and drama. Unless that's your thing. Learn to surf, take a helicopter tour, snorkel, rent a Harley (fail), see the historical sights... You could easily fill a whole month with stuff and still not have done it all.