The Windows key will usually take you back to the Metro UI screen. Such things as Winkey+Tab, Alt+Tab, and mouse in upper left corner, will give you other options.
As far as Touchscreens, you might go online and check them out. They are quite a bit more expensive than a normal monitor. Where you buy it would be your personal preference, I cannot really suggest.
Since the touchscreens are more expensive, I would think about a warranty, but if you are willing to do the job of returning the unit yourself, you might not need it. Again, your decision which might also effect where you decide to buy it.
Personally, I like Best Buy as opposed to some other places the items might be available. I seem to also have preferences as to what...