The IRS is very serious about the abuses by "hobby" businesses. As a sole proprietor you are more likely to be examined and be challenged by the IRS versus being a type S corporation. If you are considering this just as a way to write off your hobby's expenses then you might want to reconsider. You might want to start selling prints first and see how that goes. If you sell enough prints at a reasonable profit and elicit a serious positive response from people familiar with the photography market, then it might be justifiable to consider becoming a type S and opening up shop officially.
I have earned my living solely through photography for 30 years, I switched my area of interest and market about 4 years ago from advertising photography to fine art type landscape. What I have learned is that making a living through the sales of prints is not easy. It is extremely competitive, very expensive to do right and volatile. So far I have been very fortunate but I have encountered many people to whom it has been a frustrating struggle.
A side bar that illustrates a common belief, or misconception about making a living as a photographer, I think Bill Schwab can really relate to this: I was shooting in Nevada last week, (I'm in the middle of a 6 week trip out west, 6 weeks out of the 22 weeks that I will be traveling/shooting this year), it's a few minutes after sunrise and I have already been up for about 3 hours. A truck driver comes to me and starts asking me about photography while I'm setting up a shot, he's clearly indifferent to the fact that I'm busy working. He asks the obvious, what am I doing? I tell him I'm setting up to shoot a photo. He asks me if that's my job, I tell him it is. He then asks who I work for, i tell him for myself. He then asks how i make money taking pictures of Salt Flats, I tell him that my prints get sold. He then asks how do they get sold, I then tell him by galleries. He then asks what my prints sell for, so I tell him. His reaction is, "Gee I used to do some photography in High School, I should dig out my camera and start selling some photos too! I can not tell you how often this exact line of questions and entire situation happens, I should probably print a FAQ hand out to give people and save myself some time.
Anyway, the point of the story is that it is an all too common belief that making a living through the sale of one's photos is easy. It is not. If you sell prints at a low price you need to sell a huge amount of prints, and a huge amount of prints is expensive and very time consuming to produce. If you sell prints at a high price you had better have prints that are worthy of that high price or you won't sell any. My advice keep it as a hobby. If your prints start getting a serious demand, and you start making some good money from them, then consider going full time as a business.