1. Random.
2 Halloween night.
3 More candies = more prizes in the bag you choose.
4 Probably not.
5 It will not be left in game.
6 Yes.
7 There will not be heads or bodies in the Crypt.
8 Probably not.
9 Not the bowls, possibly the plates.
10 Probably not.
11 Yeah, they won't be here this year.

P.S.
For question 3, it could also be 50-100 candies = 1 bag. However I am not sure.