1st. I edited your thread title to make it clearer just what kind of tax question you are asking...
2nd. Good question. We need a tax lawyer to really answer this but I don't believe that "billable receipts" from clients require individual 1099s even if they exceed $600... unless that client is a business in it's own right, and then they would have to fill out and provide you with the 1099 which you would then use to file your taxes.
http://en.wikipedia.org/wiki/IRS_tax_forms#1099_series & http://www.irs.gov/pub/irs-pdf/i1099msc.pdf
3rd. EIN is your call. If you want to keep your photography "business" totally separate from your personal finances or have any intention of trying to "depreciate" any of your gear or claim expenses, then it is a good idea. I have not done it up to this point myself but plan to this spring as well as forming an LLC to protect my family from any losses/adverse actions against my business.
Mike
Carpe Luminous Photography
Disclaimer... I am not a lawyer nor do I play one on TV. Any advice/opinions given below are just my opinions and not legally binding.