The only questions that need answering are:
Income tax or National Sales Tax:
If it is National Sales tax, then there is only one question...
What percent will maximize revenues while minimizing the burdon on individual taxpayers.
If it is an Income Tax then only two questions need to be answered:
What percent flat tax will maximize revenues while minimizing the burdon on individual taxpayers? (The Laffer Curve, applied to flat tax) and
At what level of income (adjusted for local cost of living) should taxpayers have to make before they have to start paying taxes at all?
Of course, to eliminate "tax deductions" would greatly reduce the social engineering power of the Congress, so even though they aren't supposed to have any, they probably won't give them up easily. ;~D
(((ok CPAs, let's hear how important it is for us to keep a tax code so complicated that we need to hire someone to figure our taxes properly... ;~D )))