Hey there,
I am in the same boat, my mum and I are leaving this October for our trip *Just the 2 of us* for a girls week away. WOOOOO HOOOOO NO MEN FOR A WEEK!
We were debating earlier this year if we should go early mid or later in october or just wait until November. But we decided that early October would be awesome.
Why October is Great
The crowd levels seem to be lower as schools arent out yet for vactions yet, and people hold out until the middle to the end of October for the Trick or Treat days. Which means that the park wont be as crowded in early Oct. ALSO.... The haunted mansion is closed the last week of September for the revamp of the "Haunted holiday" and opens up again before October hits, giving you the chance to be one of the first people to ride it. Its a small world will still be up and running until the end of October, so you can still ride that before it goes down. At any time of the year, except for peak season if theres an issue, a ride or 2 maybe down, so I dont think that should damper anyone from enjoying the park. But unless theres a ride you just have to go on, revamps are bound to happen. I just think its smart to go before the larger crowds hit for the Holday season as revamps always bring in larger crowds.
But if you wanted to do the Trick or Treat days, you can always go early to mid October, get the smaller crowds and then take advantage of one of the first days of the Trick or Treat event.
Not to miss rides
What I have heard from many many people is to not miss the rides "TOT, Soarin' over California, Indiana Jones, POTC, Splash mountain, Space Mountain, Haunted Mansion, and Big Thunder Mountain. Plus the Finding Nemo Ride will be up when you get there, so thats a take in.
Where to eat
Well, i've heard that Red Rockets actually rocks, and so does Goofy's Kitchen and Blue Bayou. I've heard mixed things on Ariels Grotto for the Princess Lunch.
Early Entry
DEFINATELY DO AN EARLY ENTRY!!!!!! Apparently you can go on more rides in the first hour then you probably could all day long without having to wait in lineups. But also remember to get Fast Passes because thats a huge help. If you get to the park early, grab passes for the bigger rides such as Space Mountain, etc as some of the bigger ride fast passes for the day run out before 1:00pm.
Another thing you can look into, cause im not sure if it were just for the 50th, but if you stay at a disney hotel (and only disney hotel visitors), you can get a Mickeys Toontown madness wich allows you into the park before it opens to go to Toon town to interact with the characters and become a citizen of Toon Town for an hour.
One last thing to keep in mind too is that in October the weather is still really nice, so that is another thing you can take advantage of.
Have a great time planning your trip, thats half the fun!