amperes/ square inch for brass plating

This will depend on your exact bath parameters and desired thickness.  Current density also plays a role in the exact color and alloy composition.  Usually, the plating operator runs the parts at the required current density to prevent burning and achieve the correct base color.  You will have to adjust this by trial and error.  The amount of time will determine the amount of material deposited.  Some of this material will be removed by the antiqueing process, so depending upon the process your thickness requirements may change.

What type of product are you using to get the antique finish?  Hot alkaline?  Room temperature acid?  Something else?