Designing Business Cards For Customization

I'm really struggling with creating a template for a business card and could use some advice.  First, I added a logo and some text that the buyer can't change, they're part of the static template.  Next I add the fields where the buyer can customize their own text.  I'm doing this by adding "upload zones".  The problem is that for business cards there's no way to know in advance how large or small a field needs to be for a particular buyer, but the upload zoned are always a predefined size because there're made from uploaded images.  If I set it to allow the user to resize and reposition the upload zones, the resizing keeps the original aspect ratio, meaning the buyer can't decrease the width without also decreasing the height.

So what am I doing wrong?  Am I going about this completely the wrong way?  It seems to me that "upload zones" work fine for setting a single large area where text or an image can be added, but it seems extremely cumbersome to use them to design a business card where multiple fields need to be resized and repositioned for each individual customer.  Is there a better way to do this?  I'd appreciate some help.  It feels like I'm missing something that should be obvious.