You need to see a tax professional. Because this is a partnership, you will need to file a partnership return for the business first. That's a form included in Turbotax Business, but not Turbotax Self-employed or Home & Business. The partnership will report a K-1 form for each of you that reports your share of business income and expenses, and the K-1 goes on your personal return.
Self-Employment taxes are about 15%, they are the self-employed person's version of social security and medicare, except that while a job withholds 7.65% and matches it from their own funds, a self employed person owes the entire 15% themselves.
You owe self employment taxes on your net profit (income minus expenses) for the partnership. Then you also owe income tax on all your combined income (self employment plus wages from other jobs plus investment income etc.) minus your personal deductions and credits (dependents, property taxes, etc.).
You are required to make estimated tax payments 4 times per year to cover your tax bill. If not, you will owe penalties even if you catch up and pay in full when you file your returns. A basic estimate is 30-40% (15% SE tax and 15% or 25% income tax) but it depends on your total income, business income and expenses, and personal deductions (mortgage, etc) that reduce your income subject to income tax.
The best thing to do is get an accountant to help you set up the business. You need really good records of business expenses so you can deduct them from your income and reduce your taxable profit. Some expenses are not obvious. And the accountant can help you set up estimated taxes too.
