6 days in October - you're singin' my song! I do 6 park days, no water parks and definitely get all the big stuff done. I've traveled in sept but lately Oct and whether it's increasing crowds or just a difference between those months, park hours were longer in Oct, making it fairly easy to do "everything".
Weather is generally good, allowing us to stay in the parks all day - not wilting in the mid afternoon heat. (It still gets hot enough to swim & toasty in the sun, but nothing like July & Aug)
My kids weren't yet up to really late nights, so we didn't stay past 9 or so, but park hoppers may be a good idea if you like late nights, because depending on your dates, MK may have a couple late nights, but it will also have early closures for party nights; DHS may have some 7pm nights and some 9pm nights on your stay; AK may close as early as 5. . . You could pick a "day park" and still hop to whatever is still open later.