Drupal Commerce - How do i specify a user name for new account other than the email address on an anonymous order?
On the create user Rule you need to bring field_account_name into scope by running condition "Entity has field."

First run EHF on Commerce Order to bring the billing profile reference into scope. Then you can EHF your account name field.

You then will have the ability to have access to that field's token and use it as the new account's username.

Note: this is more a Rules usage technicality, which Commerce uses heavily.