I have a house in Florida built in 2006. The kitchen has GFI outlets. I would like to add under-cabinet LED lights. Question one: Can an additional outlet be added where I would plug in the 12v transformer for the lights? Question two: Can a switch be put in this line to turn these lights on/off? Thanks for any help.

Yes you can add a switched outlet. Very often circuits are shared for both applications, usually found in bathrooms. Make sure you run your grounds.