Customer message at checkout

You can add that by creating a custom field of the type textarea and of the table "order" via the menu Display>Custom fields in the Business edition of HikaShop.
You can even have the field for each product on the product page above the add to cart button by creating a custom field of the table "item" and thus handle multiple products purchases.

Well, you can always add the html field in one of the checkout views and handle the saving yourself with a HikaShop plugin but it's a lot of hassle compared to the custom fields solution and if you're not a developer it will be more expensive to have it done for you by a developer than purchasing the upgrade to the Business edition.
One thing to can do is to create a custom address field. The user will see it in the registration form and when editing his addresses and you will be able to see it in the order details. But it's less nice than a custom order/item fields which are really made to do what you want.

Hello,

Since that thread is 4yo and your questions are not in the same subject that the thread subject ; best would be to create a new thread.

Regards,

Hi,

It's not possible yet in HikaShop to restrict custom fields based on variants, only main products.
So the only "simple" (by that I mean without coding involved) solution would be separate your variants into three different products. You could for example have the products linked together as related products to be able to choose between the different versions of the product.