Hi,
1. The PDF invoice is only added to the order status notification email which is sent to the user when the order is confirmed. When you pay with an offline payment, the order stays created at the end of the checkout and it's the order creation notification email which is sent to the user. So it's actually the normal behavior of the plugin that you're experiencing.
If you want it to add the PDF invoice to the order creation notification email instead, you'll have to edit the invoice PDF file:
www.hikashop.com/forum/2-general-talk-ab...aching-invoices.html
2. That is not linked. If you don't receive the admin notification, it's either that the order admin notification email address field of the configuration is empty, or that you unpublished the email via System>Emails as far as I know.
3. That URL is the IPN URL of the paypal plugin of HikaShop. users should never be redirected there. You must have entered that URL in the return URL of the options of the paypal payment method via System>Payment methods (please make sure that the field is empty), or in a setting of your PayPal account.