For the redirect after login thing, go to usersc/scripts/custom_login_script.php and put
Code:
Redirect::to('http://yourlinkhere');
If you just want to add links to the current dashboard, you can put them in
usersc/includes/admin_panels.php (if it doesn't exist, create it).
If you want to completely modify the admin.php file, then you probably need to make bigger changes. The main reason is that our updates, would eventually overwrite your customizations. To prevent that, copy admin.php into the usersc folder.
Change line 21 in your NEW admin.php to
Code:
<?php require_once '../users/init.php'; ?>
Now when you go to the admin panel, you will see your custom page instead of ours and you can modify it however you want without breaking things on updates. There may be a few other things that have to be tweaked with a page as complicated as that one, but that should get you close.