Setting up shop as self employed in the US

I would strongly suggest speaking with a human accountant. I did this recently after doing some contracting on-the-side for a couple years and I should have done it sooner. It cost me something like $50 for an hour of their time and had I done it sooner I'd easily have saved $5000 in taxes. They can help you understand things like how to pay estimated quarterly taxes so as to avoid the penalty of not doing so. What you can and can't deduct (there was a TON of things I could have deducted) and how to track and log it.