Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
Yes. You can create AMP pages that use the Layout canvas for content but there are a number of considerations.
You can only add combinators to child selectors. Add a child selector and combinator will appear in the Style tree.
You don't. You apply a Descendant selector. These use a (Space).
The Youtube video embed is responsive so it should expand to the width of its parent. If you do need to set a width you can apply the Width CSS property through the Style Builder.