From what I can remember about setting up our site ...
For the name of the site see http://cambridgeopensystems.com/documentation/community/domain-name/
about purchasing a domain name. Shop around for the one you want, buy it, then get the registrar's A records for the domain to point to e-voice and update the site domain tab under website settings in Website Admin.
For the preview, make sure you have saved and picked the correct revision to preview as it is easy to end up with lots of them before publishing.
The easiest way for users to navigate on the published pages are from the menus, which are controlled by the Index tab for each page.
For more control over colours, Bootstrap has more options, and you can change from Modern.
Hope this helps get you started!