How to display public user profile with 2 additional fields? (GitHub source code included)

As a WordPress newbie I am trying to create a plugin, which will force users to specify their city and gender while registering and then display a personal profile page for each user showing this information.

I have checked in my plugin in GitHub: wp-city-gender.php.

For the registration part I have followed the Customizing the Registration Form doc and it seems to work fine – the additional city and gender fields are displayed in the registration form and stored later in the wp_usermeta table. They are also editable in the Users part of the dashboard:

Also, I redirect commenter links to /user/user_id by using this code:

define('PROFILE', '<a href="/user/%d" rel="external nofollow" class="url">%s</a>');

function get_comment_author_link($cid) {
    global $comment;
    return sprintf(PROFILE, $comment->user_id, $comment->comment_author);
}

add_action('get_comment_author_link',  'get_comment_author_link');

My question is: How can I add a personal profile page for each user, displaying his/her name and the 2 additional fields?

What I don’t want: I can not just create a plain PHP script fetching data from wp_usermeta for a certain numeric user_id – because it wouldn’t be integrated in my WordPress website, i.e. it won’t display the logo at the top and the footer at the bottom.

I think an easy way to do this would be to make use of the wordpress template structure, take a look at Codex: Templates and Codex: Template Hierarchy for a general overview. But namely you could use the author templates – Codex: Author Templates – for this, so likely you will adapt the author.php file to fit your needs.

Additionally you want to change the rewrite structure for the author template to match your goals. General information can be found at Codex: Rewrite API and Codex: Class Reference/WP_Rewrite. Besides that this has been answered several times here on WPSE, no need to duplicate this, so take a look at: Diplay a registered user profile page and/or How to custom change author base without $this->front?.