do I need to print them out on photo paper or would just a heavy card grade paper work?
Photo paper will give you a much better quality print (You have a choice of glossy or matte finish). The print will last much longer with photo paper too, but it is considerably more expensive. You can usually find sampler packs (5-10 sheets) at Staples and places like that.
Its legal to do with any of MY photos!
Did you know that most photo editing programs have special effects options which let you change the "look" of the photos so they appear to be oil paintings, watercolors, antique etc?