Number two can be addressed with something like this: https://preshing.com/20121224/how-to-generate-a-sequence-of-unique-random-integers/ https://preshing.com/2

Number two can be addressed with something like this: https://preshing.com/20121224/how-to-generate-a-sequence-of-unique-random-integers/ https://preshing.com/20121224/how-to-generate-a-sequence-of-... You can shrink the range by using a smaller prime number and throwing on out-of-range input. And then you can offset the output to make sure the base-N encoded value is always D digits long.