Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
Base styles are CSS styles for HTML elements.
You have to upload a JSON file to provide the index of the icons within your chosen icon font.
Yes, this is possible by creating a custom element.
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.