Research your states SBA(small business association) and look into what it would take to start a sole proprietorship or single member LLC(if your state offers this - not all do).
Then, buy or read this book:
How to Start a Home-Based Photography Business, 5th (Home-Based Business Series) (Paperback)
by Kenn Oberrecht (Author)
Figure out your niche in the market.
Get all your business documentation together.
Get some accounting software(Quicken has free small business accounting software that is really good).
Figure out what gear you still need and how much operating capital you will need.
Advertising?
Have all your samples and portfolios ready.
Get your pricing and product schedules together.
Have all your contracts thought out and given the once over by a lawyer.
Do you have a web presence? How will people contact you?
Also read "The legal handbook for photographers" by Bert Krages.
There is a lot involved with running a business, even one where you are the only employee.
There is more to running a business than just taking photos and running them through photoshop.
You'll need to meet with clients, be able to sell you, your skill set and your products.
Make sure that if you commit to a project that you provide a quality product that meets or exceeds the clients expectations and is on time or early.
Word of mouth will be your biggest boon or killer to your business.
Good luck with figuring out your business name and on your new venture.