You will receive a 1099 if your sales exceeded $20,000 and 200 transactions. Take note of the "and" in that statement, because the follow up question is always "well what if I did more than 20k and less than 200 transactions(or vice versa)?". The answer is 20k+ & 200+ transactions. Although you are supposed to report whether or not you get a 1099, that's none of my business.
You will file a Schedule C, refer to http://www.irs.gov/uac/Schedule-C-%28Form-1040%29,-Profit-or-Loss-From-Business for more details.
COGS is one aspect, gross sales is another aspect, selling fees & shipping is another aspect. You also can deduct items such as office supplies, shipping boxes, tape, nearly anything that cost you money in the pursuit of profit. You also can deduct $0.56/mile driven for business. You need a log for that or at the very least, some type of evidence. There is many more things
Records are extremely important. Salvage any receipts that you can. Pour through every transaction on your bank/cc statements. Figure out your expenses, because every little bit reduces your taxable profit. That is your #1 priority right now. Find every single transaction where you spent money on inventory or supplies.
I was in your shoes last year on gross sales of 360K, completely and utterly daunted by tax time(although I actually saved all of my receipts for everything.) Ultimately, it turned out to be pretty damn easy with TurboTax(provided you have records of everything....seriously, get on that ASAP). Once you get all of your expenses straightened out, you'll be fine.
yadda yadda yadda, not an accountant.