0359 is the answer. For the smallest number, always keep the smallest numbers to the left and ascend to the right.
If 0 can be counted as the first number, then the smallest number is 01358. If 0 cannot be counted as the first number, the the smallest number is 10358.
The smallest number that you can subtract from 85232 to make it a multiple of 9 is 2
The smallest four digit number is 1000. It is even so 1001 is the smallest four digit number that is odd.
It is 0.
You can make a multiple out of any number. Thus, the question becomes, "What is the smallest number?" There isn't one. Numbers continue in both directions infinitely. The smallest negative number you can think of can be multiplied by two. Then, so can that product.