Ryan:
My name is Jim O'Brien and I live in E. Sandwich (on cape cod). I have hunted sea ducks for many years on and around the cape and have all of the necessary equipment.
Eider season is open from early October till the end of January. The "best" time to hunt for them is up for debate. In October the weather can be as warm as 50-60 degrees (or even warmer) which can create a very comfortable hunt. The eider are just migrating them and large groups fly together and are typically not gunshy at that time. The cape is also a great place to visit in October with the warmer weather. The challenges are that it is still a bit "crowded" due to the nice weather and Brant are NOT open in October.
As you get later in the season, the eider and brant become more plentiful but a bit more wary and seem to break into smaller feeding groups. November the weather can be nice but starting to get cold. December and January can be bitterly cold with more extreme conditions. I would not recommend someone not familar with the ocean and the area hunt by themselves.
I am not 100% sure when brant season opens, maybe in November, I will have to check, but I know brant is open later in the season. Just for the info puddle ducks open typically for a very short season in beginning of November and are then closed until late November/early December through mid January.
I hope that I have not created more questions than I have answered but if that is the case, just let me know and I will answer. Regarding hunting, I have Eider, Scoter and brant decoys, rigged with anchors etc. I have an Estuary built by Dave Clarke and other gear as well (you can borrow anything but the boat!) You are welcome to stop by my house and borrow my gear when you are on the cape. I may be able to join you for a few days of hunting if work schedule allows. I am NOT a guide but have all the local maps and have lived and hunted on the cape for over 20 years. I have assisted other members of this forum in the same manner and they had a great time. They stopped at my house, I assisted them in getting their licenses on line, showed them on maps where they might want to go, loaned them some of my gear and they were very successful.
Again, I do not know your level of experience with boating on the ocean, but if you have limited experience and time on the water I would not recommend heading out in the fall/winter on the water on your own.
Hope all of this helps, just let me know.
Jim O'Brien