I heard they limit it to 50% capacity but the 3 times we have been its been nowhere near that, rides were all walk on and stay on if you wanted. Not been for 3 years in Oct but we went to an earlier date rather than nearer the 31st, it gets busier later in month and we also did midweek dates, they get more people to weekend ones.
We have always booked online and picked tickets up at Downtown Disney. I f you want to go on the 31st I would book ASAP, earlier dates won't sell out.
You get a wrist band when going in, anytime after 4pm. At 7pm they as anyone without a wristband to leave, everyone going on rides after 7pm have wrists checked.