Agree. Get turbotax now and do your "taxes" on it with your projected income and deductions this year, it shouldnt take that long. Then you will have nearly the exact amount you owe (depends on the inputs, GIGO). Finding out self employment tax on the other hand is also simple since you'll be maxing that out, so you pay all of that, and then add on the federal/state.
What I've done is make a spreadsheet in excel with years on the tabs, and each sheet goes jan-dec with columns for income, state tax, fed tax, total tax, SEP, bills, left over for investment.
Basically tells you everything you need to know. Now for the tax calculation I simply take the effective rate from the last year, but this does have to be changed if you have a big jump in income or something. Although after the first year if you make it to like the 33% marginal iirc, the bracket is super wide. Works great for planning and seeing how much you spend, your cash flow and what your investing opportunities are. Used with your budget and other goals and I find its my most used sheet.