Replacing the basic radio with XM... Questions

My wife and I bought our first Prius two weeks ago. We went with the basic radio system, but would now like to add XM Radio since I also have it in my car.

Is the "best" way to go back to the dealership and have the factory XM component installed? I know it'll probably be more expensive that way.

If we install any kind of after market in-dash receiver, satellite radio or otherwise, will she lose the steering wheel controls and touch screen access? Those are the two perks she's most worried about losing if we install another radio.