The things I have learned waterfowling;
1) It will be cold and raining, you will have more clothes than you have ever worn before. I wouldn't worry about a long LOP.
2) If you don't hit it on the first shot, the followup from a semi wont help. Get a pump gun.
3) 2 3/4 or 3 is more than enough. A #3 Mag in 2 3/4 works perfectly for me. Getting feathers drug through you mallard breast, when its the best tasting one you have downed all day, SUCKS.
4) Learn to identify ducks while flying. The ones you cant eat (or chose not to that is) like mergansers, still count to your limit, so save the shot...
5) Only use a dog if it has been properly trained. If your buddy says "yeah, my brother has a retriever he says is great with tennis balls!" Stay far far away. Bring a tin tippy or a canoe.
6) Ducks seem to be getting smarter, especially late season. Don't fall for the Cabelas ads that show spreads of 20-30 decoys. Where I am, 3-4 quality ones out performs a big spread of sh*t plastic ones. And BTW, the plastic ones sink when you shoot them, the foam ones don't - food for thought.
7) If it hits the water, and its close, shoot it again. Often you have just stunned it and knocked it out of the air. Steel shot misses the mark in that regard. Same reason upland guys have dogs.
Have Fun
C