No, we do not do any custom dns work. Our web control panel automates everything needed to host websites and email on our servers. Doing custom dns work negates the cost saving of having an automated system , but you can manage dns for each domain via the control panel.
Most of our clients are virtual web hosting companies. We respect our clients, which means we do not use them to sell accounts to new customers. But you can see that we provide hosting to State and country govts., Banks and corporates.
That error means that the server config has not been refreshed since the site was added. When you add a new domain, it is perfectly normal to see a 400 error or Under Construction until the server refreshes.
Yes, every domain you host at 2gbhosting can have its own cgi-bin. When you create a new domain using the web control panel, the web control panel adds a cgi-bin mapping for the new site. All you need to do to use the cgi-bin mapping is create the physical cgi-bin directory in the directory that the new site is mapped to.