I will add that unless you have some good reason for running your own name-servers on the ISPConfig box, I would just let the Web host handle it.
There are several disadvantages to the roll-your-own approach:
a.) It's complicated and it's easy to make a mistake.
b.) There are no "validation tools" within the interface that are specific to your setup (ISPConfig couldn't possibly account for that, whereas your host could, given that it's their network and hardware).
c.) If your server goes down or is compromised, you're in worse shape than you would otherwise be (the potential exists to "lock yourself out" of your box completely if the DNS server goes belly-up).