Hi,
Selecting the 1st option by default after the page gets loaded; is something we have implemented by SportMart.
In the ordinary Virtuemart, the image type custom field was not "required". We thought that, some people might add the product to cart without even selecting any option, which is why we implemented this "automatically selecting the 1st option"
I can help you here to remove that automatic selection. It is a 1-2 lines of javascript code in our template's file and when you remove those lines the automatic selection will be gone. But i can't help you here to implement the "required field" feature. Because it is little complex to implement and it is considered as a "custom modification". Unfortunately we don't provide free support or step-by-step instructions for custom coding-modifications.
You may purchase premium support:
www.flexiblewebdesign.com/premium-support
and let us take care this modification for you directly on your website though.
Regards.
Support