The Small Business Association website, while not increbibly visually stimulating, is the one site that I wish that I would have found sooner. There is such a wealth of information on tis website. You can learn pretty much everything that you need to know about starting your own small business here, get free online training, even get counseling from a SCORE counselor.
If you are even thinking about starting your own business, set aside some time over the weekend and browse around the site. It will really help you get an idea of what all is involved with starting a business.
While I am on the subject, when you are planning to start a photography business (either part or full time) I really recommend that you give yourself at least a year to do all of your planning and research. That may sound like a really long time to you, but especially if you plan to keep your full time job in the mean time, it will probably take you that long or longer. You need to do market research, determine your niche, develope your product lines, design your marketing materials, set up your businesses legal structure, get permits and licenses, put together your portfolio, design and produce studio samples, find capital....get the idea? That's not even a full list.
Another thing to keep in mind, the first few jobs that you get are really exciting. You come home from your day job and sit at your computer until you go to sleep at night. That feeling will not last. Trust me. You need to plan some "you" time in your weeks and weekends otherwise you will burn out big time. You will also be spending a lot of time NOT taking pictures while you are getting everything set up. You want to start a photography business to take pictures, I know, and you will - just not at first. You need to send the time planning so that your business will have a strong foundation. The better you do at planning and organizing now, the less time you will have to devote to it later when you are out taking pictures. It is a lot of work up front, but if it is what you want to do, it will all be worth it.