If I understand correctly you have nine days (including travel days? maybe only seven days?) and want to visit four islands. I'd cut that down and stick with two to three islands. Oahu will give you beaches, shopping and hiking (some good ones on Diamond Head). I wouldn't spend more than three days. Kauai offers excellent hiking in Kokee State Park and other places. There are also fabulous beaches but you'll find little in the way of shopping and restaurants. It's by far the quietist of the islands you mention. Maui offers lots of everything - restaurants, shopping, beaches and some hiking. The Big Island also has a great mix and you can see the lava flow. I wouldn't want to move around quite so much, but would pick two islands that seem to offer most of what you're looking for. Once you've picked the island you should have no problem finding hotels in your price range and cars that you can rent.