We plan to start our three month eurail global pass from Stockholm with the first journey to Amsterdam. Has anyone done this journey with or without a eurail? Would it be worth stopping in Copenhagen at the end of October to break it up? Or should we do the whole trip at once? Has anyone started their eurail pass in Stockholm?
Have no idea what you mean by starting your eurail. Unless you mean using a rail pass. What are you asking?
I also don't know what you mean by "Has anyone done this with or without a eurail?" A quick check online shows anything from a 21 to 25 hour duration of train travel between Stockholm and Amsterdam. I would recommend breaking it up into at least two legs. Stockholm to Copenhagen lasts about 4.5-5.5 hours, and that's probably good enough for one day's travel. After that, perhaps consider Hamburg, Bremen or Lübeck before continuing on to Amsterdam.