1. I have only flown on DL to the islands, but it is normal domestic service, with a meal provided in coach class. First class is the standard domestic set-up. Whether it is worth it or not depends on how long you can stand sitting in coach. If flying from LAX, the flight is not that bad in Y. From ATL is a different story. You can upgrade with miles on a K fare or higher, yes. There are no complimentary Medallion upgrades to Hawaii.

2. YMMV, but I have never had success booking at the low availability level.

3. Yes.

4-5. No experience with AA.

6. I generally pay unless I want a confirmed F seat. Like banking the MQMs.