Techniques for setting up a web application's presentation layer

I am working on a Ruby on Rails web application, although I guess it should not matter too much what my backend layer is.

I am currently evaluating ways for my application to elegantly handle the UI layer in terms of ease of use, ease of making things actually look good, and also have sound architecture. Here are my questions:

1) When is it a good idea to use a CMS like Drupal or Joomla?
2) If I did use Drupal for example, would it work awkwardly with an RoR app since I'd need Apace server to host the Drupal probably? 3) How do I elegantly design my front-end layer to in the future enable heavy JS integration, possible HTML5 if needed, and a nice way to handle various divs interchangeably?

Thanks and sorry for the long-winded questions :)

1. When you have a content oriented application
2. Drupal is in PHP. It will very hard to make that play nice with RoR. You have have Apache/nginx to host both RoR and Drupal on the same host (different ports)
3. RoR is a MVC web development framework. It means that it has a clear separation of Models (data), Views (UI) and Controllers (logic). Start coding in RoR and you'll see how grate it is.

I strongly suggest starting with Rails 3 and using something like Railscasts to learn.