Paying in quarterly estimates just to get them back at the end of the year (without interest ) is not a good idea ...put the money into a savings account instead.
Here is some good reading for the self employed :
Publication 463 Travel, Gift, and Car Expenses
Look at the chart on page 12:
https://www.irs.gov/pub/irs-pdf/p463.pdf
IRS information on Self Employment….
http://www.irs.gov/Businesses/Small-Businesses-&-Self-Employed/Self-Employed-Individuals-Tax-Center
Publication 334, Tax Guide for Small Business
http://www.irs.gov/pub/irs-pdf/p334.pdf
