Hi,
You can't "load 5 products into the page".
However, if you want to have extra input fields based on what is select in a field, you can use the "display limited to" setting of your custom fields.
So, now that you've created a custom field to select the number of pieces, you can create another field, and in that new field, you can use the "display limited to" setting to restrict its display based on the value selected in the first custom field.
This way, you can chain custom fields and provide several sets of custom fields if necessary.
Then, if you want the price to vary based on the custom fields, you want to use the price calculations plugin, as I was saying.
And regarding the canvas, if you want it to replace the image area, then in the show_default view file (via the menu Display>Views, as I was saying), you can remove this code:
$this->setLayout('show_block_img');
echo $this->loadTemplate();
And add your canvas code there instead.