Adding an optional feedback text box to an order

Hi,

You can add a text area on the checkout by creating a new custom field of the table "order" (Business edition only) via the menu Display->Custom fields.
However, that custom field will be for the whole order, regardless if it contains that product or another one.

Alternatively, you can add such field on the product page by creating a new custom field of the table "item" (Business edition only) via the menu Display->Custom fields. You can restrict it to only some categories of products. That way, your customers would add the information directly for the products which need it and not see the custom field when it's not needed. That also allows him to add different information for the same product if he buys more that one of it.