re: If America were to implement a flat income tax what would it need to be?

Zero. No income tax on people or company profit.

value added on goods.
.1 Per cent of all computerized market sales like NYSE and commodities exchange.
(Besides income, Perhaps this would cut into computer programs driving markets into the ground).
Fuel tax similar to current
50% of estates over 3 million.
1% of real estate sales that are flipping ie refunded only if you live in it for 2 years+.
Whatever is legal re imports.