No. Your initial capital is your investment. You can not "calculate" it, it's determined by your wealth, not by your strategy performance. It must be above the required capital without reinvestment, but by how much is up to you.

You must only observe the equity curve and check if it becomes negative. It should not. If it does, you're reinvesting too much. You should then change not your capital, but your reinvestment formula. You're not supposed to maintain money to remargin.