Debian for ISP

[Omar <alienonearth@spymac.com>]

Hello all,
  I have just took over a network for an ISP that is running Debian, I am used to
using Cpanel/Whm and now I have to use the CLI.

The ISP also provides Hosting services and it uses dbdns 1.03, tinydns, xfrdns, I
am having problems with tinydns, as I use the add-ns and it worked for 4 domians,
and then I can't add anymore?  Is there another way around it?
Also I want to ask if there is a way that I can check the user Authentication? 
Or get a list of users and their level? admin, regular user and so on.  I believe
that the previous admin used LDAP, is there a way I can look into the LDAP
database and find out the users and their levels?

Also I am thinking of installing webmin, so I can configure everything over the
web, if I do install it, will it recognize the current system, and the current
settings or will I have to take things in manually.

Thanks you all in advance.....