If a company makes products entirely out of plastic, could it still be eco-friendly? why or why not?

It depends on what kind of plastic the company uses for making its product. If the plastic is recycled plastic, then yes it could; as part of the goal of green design is to use as few resources as possible, a discarded item could be used to create an entirely new product.

Any product that requires energy can be made green, so a product could be also eco-friendly if the resources and energy are used efficiently.

It all depends upon the environmentally conscientious process.