1. You should leave that option turned on.
2. The Thank you for your order page should redirect you to the default "normal" thank you page of HikaShop.
There is actually a glitch in the plugin.
The line:
$return_url = HIKASHOP_LIVE.'index.php?option=com_hikashop&ctrl=checkout&task=after_end&order_id='.$order_id.$this->url_itemid;
should actually be:
$this->payment_params->return_url = HIKASHOP_LIVE.'index.php?option=com_hikashop&ctrl=checkout&task=after_end&order_id='.$order_id.$this->url_itemid;
in plugins/hikashoppayment/authorize/authorize.php and it will work properly.
3. In that case, if the redirection doesn't work, it means that the mootools library is not loaded on your website
Add the code:
if(!HIKASHOP_J30)
JHTML::_('behavior.mootools');
else
JHTML::_('behavior.framework');
before
$doc->addScriptDeclaration("do_nothing( function() {window.location='".$this->payment_params->return_url."'});");
in plugins/hikashoppayment/authorize/authorize_thankyou.php and that should make it work.
Regarding the order page, you could enter the URL of the user's order listing (you can create a menu item of the type HikaShop order listing via the menu manager to get the URL).