Hi,
As you have probably already gathered from the previous responses, the Internet is the wrong place to get good advice about a lot of this, beyond the general answers to talk to an attorney and a CPA.
That's because it varies a lot, place to place.
You probably need a business license, but local requirements are different everywhere.
How to structure your business has to do with taxes, employees (or lack of) and legal liabilities. The lawyer and CPA are your best resources to get those answers.
I'm not familiar with legalzoom.com, aside from having heard the name a few times. Frankly, I'm not entirely comfortable with an Internet based legal resource for this sort of thing, since there are often local, regional and state level nuances that you really need to take into account.
Professional associations can provide a wide number of benefits. I'm not a member of PPA, but am a member of NANPA. Explore the various photo-related associations, find out what's active in your particular area too, then make a choice or two. Some of the benefits may offer enough savings on things like group insurances to easily justify the annual dues.