Becoming an independent contractor. I need advice re: expenses, credit cards, taxes

I've done independent contract / freelance work for years, but only in an 'on the side' basis.



Well my 'on the side' work has grown into a highly demanded skill, and a company wants me to work for them 20 hours a week minimum as an independent contractor, with this and my existing 'side work' I'll be transitioning to full-time as an independent contractor working for myself.



So.... it's time to officially start treating myself (and my skill) as a business.

This leads to a few questions:

• Do I need a business license if *I* am the business?


• How do I figure out how much tax I'm supposed to pay and how often do I set those taxes aside?


• I think opening a 'business credit card' and using Mint.com will be the best way to track my business expenses for my end-of-the-year taxes. If I get a credit card that I only use for business expenses (cell phone, software, equipment etc.) then use mint.com to have a detailed list of the expenses for THAT CARD alone.... Is this the best way? And if so:
  
  --A. How much of those aforementioned taxes can I deduct (i.e. how much of my expenses can be deducted)?
  
  --B. What is the best credit card for small businesses? I already have a personal American Express card I'm thinking of just converting to a business card (I don't like having a bunch of cards).


• Thankfully it looks like my insurance will not need to change, but are there any other federal, financial or... well really any downsides or pitfalls to being a full-time independent contractor that I don't know about or should prepare for?