Any guides on creating custom admin pages?

I pretty much started in the same place as you a while back, and have created something similar. Here’s what I think you need to know.

1) Work out how to create your basic hello world first and foremost. A simple plugin will consist of a few comments at the top of a PHP file dropped into your plugins directory. Notice the variable calling the class which gets it moving. Constructor of the class calls add_top_level_menu, when this is clicked on (see $function variable) the display_page() function gets kicked off starting to build out your page.

<?php
/*
 Plugin Name: Your plugin name
 Description: Description
 Version: 1.0
 Author: Your Name
 Author URI: http://yourweb.com
*/
$myplugvariable = new yourpluginname();
class yourpluginname
{
  function __construct(){
  add_action( 'admin_menu', array( &$this, 'add_top_level_menu' ) );
  }

  function add_admin_scripts(){
  //adds javavascript files for this plugin.
   wp_enqueue_script('my-script-name', WP_PLUGIN_URL . "https://wordpress.stackexchange.com/" . dirname(plugin_basename(__FILE__)) . '/js/javascript.js', array('jquery'), '1.0');
   wp_localize_script('my-script-name', 'MyScriptAjax', array('ajaxUrl' => admin_url('admin-ajax.php')));
  }

   function add_top_level_menu()
   {
        // Settings for the function call below
        $page_title="Plugin Name";
        $menu_title="Plugin Name";
        $menu_slug = 'plugin-name';
        $function = array( &$this, 'display_page' );
        $icon_url = NULL;
        $position = '';

        // Creates a top level admin menu - this kicks off the 'display_page()' function to build the page
        $page = add_menu_page($page_title, $menu_title, $this->capability, $menu_slug, $function, $icon_url, 10);

        // Adds an additional sub menu page to the above menu - if we add this, we end up with 2 sub menu pages (the main pages is then in sub menu. But if we omit this, we have no sub menu
        // This has been left in incase we want to add an additional page here soon
        //add_submenu_page( $menu_slug, $page_title, $page_title, $capability, $menu_slug . '_sub_menu_page', $function );


    }

    function display_page()
    {
        if (!current_user_can($this->capability ))
        wp_die(__('You do not have sufficient permissions to access this page.'));
      //here comes the HTML to build the page in the admin.
      echo('HELLO WORLD');

    }


}

?>

2) Once you’ve created internal functions to return your data, whatever that may be. (use global wordpress data functions, e.g. $wpdb->get_results($sql).

3) AJAX inside the admin is a bit different to how you normally use it. All wordpress AJAX calls hook into admin-ajax.php. I found this: http://www.garyc40.com/2010/03/5-tips-for-using-ajax-in-wordpress/#js-global quite good at explaining things.

4) If you are creating tables: something like the below will do the work for you. search for dbDelta in the codex.

function plugin_install() 
    {
    global $wpdb;
    $table_name_prefix = "plugin-name";
    $table_name = $wpdb->prefix . "plugin_name"; 
    $sql = "CREATE TABLE " . $table_name . " (
         id mediumint(9) NOT NULL AUTO_INCREMENT,
         post_id mediumint(9) NOT NULL,
         score mediumint(9) NOT NULL
    );";
    require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
    dbDelta($sql);
    }