I'm afraid you shouldn't actually put much stock into that, actually. It happens every new gen or in fact Pokemon game: a website or game store will state that the game is coming out on a particular date. Then another one will soon give a different date. And so forth. And in the end all the guesses by the stores are wrong and the game comes out on a different date.
It's common practise, really. You'll be sure of the date when Nintendo themselves announce the release date, which probably won't happen for some months yet. I believe the Halloween date is just picked by Gamestop for the time being as all we know is that it is in 'October', and that is the last date of the month. (Typically major dates like Christmas have been picked by stores for instance, despite the lack of any Pokemon games ever coming out on that date for at least many years if ever).
As there's not much point in discussing a date that's probably not correct, going to close. Anything else you mentioned there is covered in existing thrads too (e.g. the 'which game would you get' question).