Use a child theme for storing CSS?

I am getting ready to re-design our organizations web site in WordPress and have a few questions that will help me get started.

1. From what I read, you don't need a child theme to preserve the options you've changed when Atahualpa is updated - as the changed options are preserved. Is this true?

2. If I am going to edit the CSS for styles, etc. would a child theme be what I'm looking to create? Or would these CSS changes also be preserved when the Atahualpa theme is updated?

3. I've read the Atahualpa 4 will be a responsive theme - is this correct? Any timeframe for when it will be released?

Thanks for your answers.