We were there Oct 21 - 26 this last year.
It was fairly busy due to the fact that many schools have fall break during this time of year, and also because of the Halloween party at DCA and all the new Halloween decor in the parks this last year.
However, even though it was busy in the parks and the lines looked VERY long, the wait times were incredibly fast. We usually only stood in line for about 10 minutes, and that was in the regular standby line. They were loading and unloading the rides very effeciently, and therefore the crowds were no problem. It was our best trip to DL ever!
The weather that time of year is usually comfortable and warm during the day, but it can get a little chilly in the evenings. This last October when we were there it was HOT, hovering around 90 degrees during our whole trip, but that's unusual. Temps between 75-80 is more the norm I think.
We'd definately go again in October - it's a great time to visit!
Your plan is perfect. Monday thru Thurs will be slower days and you should be able to easily get LOTS & LOTS done. You'll be able to ride to your hearts content! Then, by the time Fri & Sat roll around, along with more crowds, you can slow down a bit, sleep in, do some shopping in DTD, go swimming, maybe watch a show in one of the parks that you haven't seen yet, and stake out a great spot for watching the fireworks. Have a GREAT TIME!