I have 5 Borders Gift cards ($65?) that I want to use on Amazon for non video/book items. Am I able to buy something, then return it and purchase an item on Amazon with the new email gift certificate?

"Returns of merchandise purchased with a Borders Gift Card will be credited in the form of an Amazon.com e-mail gift certificate. If any portion of the purchase of a returned item was applied to your credit card, we will issue a refund for the same amount."

looks like you could

I don't think you're allowed to use more than one borders gc at a time.

And does anyone know if you can get the STL price when you pay with the borders card?

You can combine Borders GCs at Borders stores. You can get the STL price with a Borders card, but you cannot give Love while at Borders.com.