How to achieve sequential & custom numbering on the balance forward bills?

Summary:

We are implementing Balance Forward Billing and see that the bill numbers are generated in double digits(13, 14, 16 etc) for one month and during the next run the numbers are directly jumping to 4 digits(4001, 4002 etc).

We are looking for answers on the following questions :-

1) Is there a way to get sequential numbering on the balance forward bills?

2) Is there a setup that can be controlled to use our own numbering system, like a number that is in specific digits and starts with a specific number?

3) If the above is not possible through configuration, can we implement it through any technical intervention?