Change admin startpage to Pages-page?

This should work for you if you put it in your themes functions.php file, but you may want to modify the conditions, and the url to redirect to depending on your set up.

function loginRedirect( $redirect_to, $request, $user ){
    if( is_array( $user->roles ) ) { // check if user has a role
        return "/wp-admin/edit.php?post_type=page";
    }
}
add_filter("login_redirect", "loginRedirect", 10, 3);

Here’s a link containing more info about using the login_redirect filter:
http://codex.wordpress.org/Plugin_API/Filter_Reference/login_redirect

There’s also a few login redirect plugins floating around if you do a google search.