My final suggestion to you, is that if you really own chelsev.com, is to use the feature on 1and1 to use THEIR dns servers (at least until you have entirely configured your server) and create an A Record to chelsev.com pointing to your fixed IP address from BT, and then a subdomain A record to www.chelsev.com
... And then proceed with your ISPConfig installation. Otherwise it will simply not work as ISPConfig checks that the world sees the main host as an IP addr on your machine during the install process.
Then and only then, configure a domain to set up as a "host domain" on your favoriate registrar that allows for such (basically any except 1and1, as I covered in the other thread). All you have to do to configure ns1.something.com to resolve to your machine as a DNS server is to configrue it as a "host domain" with your registrar. That is all. Nothing in ISPConfig, no A-Records, nothing else.
Also a little note:
Whatever address you intend to direct users to for the ISPConfig panel (if that's only you, or many) you should probably want to make sure and have it be perfectly the same in your certificate or else many browsers give the "danger bad certificate" warning, instead of just simply the "unknown authority" warning!