How do I determine my burden resistor for my current sensor?
Ohms law applies as long as the transformer is operated well enoug away from saturation.

At 150 mA to get 12V you need R = V/I = 12/0.15 = 80 Ohms. 
12V is getting moderately high for some CTs (current transformers) - you should check the specification sheet to see if there is a stated upper limit.

If max current is 30A (RMS rather than peak) then the peak current will be 1.414 (= sqrt(2)) times as high for a sinewave and you need to reduce your burden resistor accordingly if you want 12V max. ie Rb = 80/1.414 = 56.7 Ohms. Using somewhat less than the calculated values will give a proportionately lower voltage and allow you some safety margin for waveforms that are non sinusoidal for whatever reason. If your waveforms have been badly distorted by equipment such as switching power supplies or reactive loads or loads with poor power factors you may wish to use a significantly lower burden resistor to accommodate semi-artbitrary waveforms within your ADC's input range. 

If you are feeding this signal to an ADC to measure the waveform voltages as the current changing then you do not want to add anything that distorts the waveform significantly - which is what a filter does by definition. The same applies to a regulator. If you want to only measure peak values or mean values or some other related measurement then you need to provide more information.