Using mult-site?

I have created one website using the mult-site feature, With the mult-site feature, I would like to create similar sites (same design/functionality), of course the content and navigation menu will end up changing. As a result, I have a few questions and/or concerns:

-Is it possible to create a template from a theme that could be applied to various sites in the network?
-At the current moment, the main domain,, has a static page which I would like to keep. As a result, I would like to create a sub-domain, to begin creating the website so that the static site is not taking down? After, I'm finished with creating the development site, I would like to replace the static page with the full WordPress installation. So far, I've created a sub-domain in the c-panel but am not sure if I would be able to change the sub-domain to the main domain after I am ready to launch the site.