Hi,
1. Suppose that you enter in the custom item field the URL of the custom image that you created:
mywebsite.com/mycustomimages/custom_18.jpg
And suppose that the column name of the custom item field is "custom_image".
Then, you can edit the file "cart" of the view "checkout" via the menu Display>Views and add such code:
<img src="<?php echo $row->custom_image; ?>" />
somewhere after the line:
<tr class="row<?php echo $k; ?>">
Similar code change are possible in the invoice or the order details page views, the emails, etc.
2. The link I gave earlier
www.hikashop.com/forum/2-general-talk-ab...ct-fields.html#19870
explains how to add a custom item field value to the product in the cart via the add to cart HTML link. So just follow my explanations there and you should be able to add the URL of your custom image easily.
3. Regarding the email sending, it really depends what you want.
At first, you talked about sending the email when pressing the add to cart button (so before the checkout).
Now, you're talking about sending the email at the end of the checkout steps (so before being redirected to the payment gateway).
But is that what you really want ?
Don't you want to send the email after the payment notification when the order is confirmed ?
Suppose that it is the last case, you could just edit the email "order status notification" which is sent to the user when the order is confirmed via the menu System>Emails, and add your own call to the mail function in order to send what you want where you want.
An even easier solution would be to just enter the email of your sales department in the "bcc" field of the order status notification email so that they would get a copy of the email which is sent to the customer when the order is confirmed.