Is Twenty Eleven a responsive theme ?

kind of tutorial instead of constant asking

See: http://codex.wordpress.org/
It’s not theme specific, but it contains tons of useful info.

‘bullet-proof’ configuration

Realistically, no such thing – anytime you make a change, it’s possible to inadvertently mess something up. However, learning how WP works and following advice given (i.e. use a child theme, don’t randomly decide to edit a theme file, don’t install themes or plugins from unknown sources)

If you want less chance of messing up your site and fewer back-end responsibilities, staying with WordPress.COM would be the better way to go.

You can post a new thread about that: http://wordpress.org/support/theme/twentyeleven#postform