Hi,
1. That error is displayed when custom fields are not provided even though there are their.
Remove the view "fields" from the "checkout workflow" setting of the HikaShop configuration and that won't happen.
2. You can disable the "order creation notification" (for the user) and the "order admin notification" (for the admin) via the menu System>Emails.
That way, the customer will get the "order status notification" and the admin will get the payment notification email when the order is confirmed (after the payment).