Craft show income, expenses, taxes

Hello!

I've just started doing craft shows in the state of WI.  I have filed for a state seller's permit.  I plan to do 4 shows total this year.  I called the Department of Revenue and know that I need to pay sales tax by Dec. 31 on all of my sales.  What I'm wondering is what I need to know regarding my income taxes...do I claim all sales as income no matter the amount?  Can I write off purchases (furniture, equipment, supplies) for my in-home studio?  I should note that I am a business, but far from profitable.   Thanks!