Told you I was old, or at least getting there!
About the paper issues for the graphics. There are many alternatives about where to purchase them. You can buy the paper at retail stores, like Wal Mart, or online at auction sites. Oriental Trading company will have some good deals on the paper, but unless I key worded wrong, I have not found a big selection.Another place is craft stores, it will be more expensive, but in the scrap booking section there is a lot of choice, at least I have found that to be true.
You can buy from scrap booking places online that are individual artists with their own websites. They usually require that you leave their copyright mark somewhere on the page. I have done that, but it is not my favorite choice. Kids can be inquisitive, but I do understand the artist needing to protect their product too. Also, they do ask that you link to their site, or even acknowledge their work somewhere on a website.
Another way to do it for paper, is to buy from a home office store, they sometimes have a good selection. You might find that some customers want a heavier type of paper,so a card stock that works with your printer is another option. You can use glossy if the printer can print that way, a lot of people will make the keepsake by either framing them, or putting them in a scrap book.
Side note about the folding of paper, if the customer wants to keep it unfolded, you might want to get larger file type envelopes to use. Again, think of the cost that it will add to your business. (Just thought I would throw that one in.)
With a good graphics printer and a graphics editor, you will not need any specialty paper with colored or pre printed designs on it. All you will have to do is to find a border the color coordinates with a theme and the primary graphics used. Again, make sure that it is one appropriate for print use, or for use on your web page.
Well, that is all that I can think of for now.
Old Mom