Generally speaking, most people don't set aside one whole day for CA.Adv., but rather hop back and forth between there and
Disneyland on some or all of their days. I like to start my day at DL, then head over to DCA sometime between late morning and early afternoon as the crowds pick up. DCA is pretty much never as crowded as Disneyland so its nice sometimes to escape the crowds and go over there for some rides and maybe lunch. So we may spend a few hours over at DCA or just an hour, then take a break at our hotel or head back to Disneyland. Now if you have some sort of ticket that isn't a hopper (not sure they make those anymore so this may be moot) then I would think a day would be enough to see and do most of what you want to do.
To me the must see's at DCA are:
Aladdin Show (do not miss this)
Soarin
Grizzly River Run
Monsters Inc.
Turtle Talk with Crush
California Screamin
Its Tough to be a Bug (3d show can be too intense for little kids)
Animations
Tower of Terror
The rest of the rides can be quite fun but are more along the lines of what you would see at any amusement park and therefore if you are low on time should probably be seen after some of the unique to Disney type rides. If you have little kids, the Bugs Land area is very fun for them, its geared for the 3-6 set.
October is more busy than it used to but not as crazy as Christmas week, Spring Break or summer. Any weekend, any time of year will be very busy at Disneyland. If you are going near Columbus Day that may also affect crowds. There is Mickey's Halloween Treat now at DCA during October and that can bring in crowds too. However in all, if you get to the park at opening (mornings are always less crowded) you can have some great hours to see quite a bit before the crowds arrive.
Have fun in Disneyland!
