How do I determine terminal characteristics of a dc motor with known torque and angular velocity?
There are four major (electrical) parameters that are used by engineers when selecting a brushed dc motor: The torque constant (Nm/A), the "back-emf" constant (V/(rad/s)), the armature resistance (ohms), and the armature inductance (H).  Normally the inductance is low enough that it is ignored.  By some fluke of units it turns out that in the SI system the newton-meter/amp is numerically equal to the "back-emf" which is simply the volts/(radian/second) of rotation.  When a motor spins it generates a voltage which is called "back-emf". This happens even when you are using the motor to generate torque by applying a voltage.  The result is the faster it turns, the less current flows until an equilibrium is reached.  More here:

http://ctms.engin.umich.edu/CTMS/index.php?example=MotorSpeed&amp;section=SystemModeling

The result is you can estimate the voltage the motor will produce at a given rotational velocity (Volt/(radian/second)).  However, the actual output of the motor is going to vary a ridiculous amount so it really can't be depended on. Your best bet is to find an appropriate dc-dc converter that takes the nominal voltage of the motor as the input and outputs your desired voltage.

http://www.cui.com/parametric-search/power/dc-dc-converters

Also don't forget about the armature resistance that will limit the total power available.