If you decide to use a professional service one day, Becca, it might be worth looking into vinyl stickers as well. High quality ones are nice for their ease of application/removal from a variety of surfaces. Also, if in the future you wanted to draw larger and more complex scenes with your characters, they'd be great for room decor.
This is also only my own opinion, but due to the high demand for your designs, it might be worth making collectibles. Something like trading cards that you could break down into series', so that you can always be making what you want to make. I think using a professional service would become necessary in that example. But, with some strategic planning and marketing it could be a huge success. In general, I think trading cards that are part of a game are more successful then nostalgia. But, it may be worth testing the waters with something simple and seeing if you enjoy it.