CCS/INSTASPIN-BLDC: doubts about FOC for BLDC

Tool/software: Code Composer Studio

Hi,

I just attended a video lecture series (Part1-2) by Mr. Dave Wilson, Teaching Old Motors New Tricks on youtube. Amazing workshop. Thanks a lot TI, for providing such wonderful learning materials.

I will be thankful if someone can answer my doubts. 

1. What is the simplest method to measure the direction of the current in the motor winding? Mr. Dave has mentioned, put some small resistor in series. But if the current direction changes the voltage across the resistor will be negative and the microcontroller may have an issue to read the negative voltage. 
2. For FOC, what motor transfer function should be used to design the PI controller? Mine is single pole brushless DC motor. I am confused with the Alfa-Beta and rotating frame park transformations. Does it affect the loop transfer function?
3. Do we really need PWM on the Phase C? Current will be always summation of the Phase A and B. Depends on the direction of the summation, either I have to sink the current or source the current. And current is already regulated on phase A and B, why do I need to regulate the phase C current?

Thanks