We just went the 1st week of May when I was about 7 months pregnant (29 weeks). We spent 3 days in the parks and it was wonderful! It was in the 90s and the heat was tough but I don't think you'll have that problem in Oct. The walking was do-able I did drink lots of water, take several breaks and did 2 sit down meals per day. The middle day I went back to the hotel for a 2 hr. break and changed my shoes and that helped a lot.
I was able to ride everthing my 3 yr. old rode (she is not into Matterhorn, Splash, etc yet) but Pirates, HM, all of Fantasyland (besides Matterhorn) I was able to do, just be careful when they pull down the bars, lol!
It was a great trip and totally worth it to spend the time w/ my 2 girls! You'll have a great time!
*Oh I just saw you asked about flying, we flew from San Antonio so it was about a 3 1/2 hour flight. I did fine on the way out, but on the way back my legs and feet did swell quite a bit. Be sure to get up and walk around every hour or so and drink lots of water. I elevated my feet as soon as we got home and I was fine the next day.