MK, Epcot & DHS all offer special fireworks for NYE. Don't know where you are staying or what time you'll be getting to WDW, but you may not be able to get into MK as I hear it tends to get so crowded that they stop letting people in. I also heard that they do usually reopen later in the evening, since people start to clear out after dinner, but I don't know for sure. Don't know if DHS fills to capacity or not.
We usually go to Epcot since we prefer to toast in the NY & MK doesn't serve alcohol. We got smart last year & went later in the afternoon after we had a nap. We made ADRs at Nine Dragons since Chinese food is a NYE tradition for us & we really like there, even though it doesn't get the greatest reviews. We got in later in the day no problem & after dinner we just walked around for a while. They give out free hats & noisemakers & they have a different stages set up throughout Epcot with different performances.
If you do decide to go to Epcot, you will not find any upfront spots around the lagoon if you arrive later in the day, because people camp out there very early & hold their spots w/ blankets. If you find a fountain, wall, steps, or whatever to stand on a ways back from the lagoon, you still should be able to see okay, but you better stake your spot about 2 hours before midnight.
As for the luau...in all the years we've been going to WDW, we've never been. It doesn't get the greatest reviews here on the DIS, not thrilled w/ the menu offerings & we just have so many favorites that we've never had the desire to eat there. You can do a search & see pictures & reviews from others that have eaten there. Have fun!
