To answer your first question, the numbers used for numbered lists don't matter. This

    1. One
    1. Two
    1. Three
    1. Four
    1. Five

Gives 

1. One
1. Two
1. Three
1. Four
1. Five

Don't believe me? Read the source for this post: http://meta.stackoverflow.com/revisions/06511612-1c2a-4d21-a5fe-6edaec15770d/view-source

------

Using `#` would conflict with headers. Also, one of the main benefit of Markdown is to be extremely readable and intuitive. Having `#` turn into numbers is in my opinion far less intuitive than creating lists from, uh, numbers.