Ended up with this, hope it helps someone.
Add to functions.php of your theme
add_action('user_register','my_function');
function my_function($user_id){
$user_info = get_userdata($user_id);
$username=$user_info->user_login;
// create a category with username
wp_create_category( $username );
// create page with username and theme?
$my_page = array(
'post_title' => $username,
'post_content' => '[list category='/$username/']',
'post_status' => 'publish',
'post_type' => 'page',
'post_author' => 1,
'post_parent' => 105,
'post_status' => 'private',
);
$newPageID = wp_insert_post( $my_page );
update_post_meta($newPageID, "_wp_page_template", "cliente-portal.php");
}