We were there last year the first week of October. We left on Saturday before Columbus Day. We noticed crowds increasing on Thursday -- still not really bad, but larger than they had been all week. Friday was our "down" day, where we went to BB, DTD, and then we went back to MGM to see Fantasmic! one last time. We did wait for nearly an hour for the show, but had no problem getting great seats. We also went back to MK on Saturday morning for one last time. Getting there at opening, we had no problems getting on rides. DS & I rode the Buzz Lightyear ride 3x walk on, while DH & DD rode Space Mtn. They didn't have much of a wait either. By the time we left, around 11:30, it was getting more crowded. My advice would be the standard -- get there early and use Fastpass.
Have fun!
Christy