Should I get my business license?

Hey everybody. Right now I work a full time job as i purchase all of my necessary equipment and save enough money to get my automotive business going. My question is, should I get my business license for the side jobs that I do? I want to keep everything legal, and also, the tools that I am purchasing aren't exactly cheap. A friend of mine told me that if I got my business license and filed taxes accordingly, that I could write off my tool purchases. I only make a few hundred dollars a month doing my side work, so would it be worth it to go ahead and get my license? I am planning on having my business up and running in the next 6 months. Thanks for any help.