As far as what days to go to certain parks, that is hard to tell, because it depends on your taste and how you want your vacation to go. But for me...I don't really prefer the crowds, but sometimes are unavoidable, especially in WDW. But from what I hear October is a very slow month, and you probably won't have a problem with crowds if you were to go in like in July or August timeframe.
I would think the busiest day of your trip will be on Saturday, but then usually Sundays are pretty quiet, especially in the mornings. I usually plan which park I want to go to based on the day they are open the latest. And if the crowd is too much for you at one park, you can always hop to another and check it out. Or go back to the hotel for a break/nap.
Have fun!!!