Those features aren't built-in — however it's all done in PHP code, so you can modify it to pretty much anything you want. As long as you can structure the logic of the code, a coder can make it happen.

Built-in, there is a volume discount for shipping — but not the product price itself.

A discount field is certainly possible, however I don't have the code to provide for it.

Anyone with basic PHP coding abilities shouldn't have trouble doing it. It would simply be adding a form field to the product details page, adding another one to the backend admin page, and then modifying the shopping cart file "cart.php" to perform the discount. Not too difficult, but you've got to know some code — or have an outsourced guy.

You'd probably have to hire a freelance coder to do it for you.