function to include is_home, is_archive, is_category, is_author etc in one function?

Based on what you described:

function is_blog()
{
    return ( is_home() || is_single() || is_category() || is_archive() );
}

And then just call the is_blog() function whenever needed.

I also found this, which looks like a more specific way to do the same thing https://gist.github.com/1189639