Ken: With respect to what you are planning for the grounding, it is not a good idea to split the ground path to two separate points. First, it's against code. All grounding conductors must run side-by-side with the current-carrying conductors back to the system ground at the service. (A ground is one point only). Second, by splitting the ground, you can create voltage differences which may lead to common noise - making matters worse not better. Off the record, the best way to ground is by routing the conductors to a ground near the outlets. However, this is dicey with respect to safety because a spike or a fault could sneak by the circuit breaker causing damage to equipment. Take the green branch circuit grounds back to the subpanel ground bar (use a separate neutral bus for the whites) and then use the raceway back to the service panel as the last leg of the ground path. This, IMO, will give you the best performance.
As far as twisting the branch wiring, I think it's a very good idea, especially for high current draw equipment (I have done this for my dedicated amp circuits). The thinking behind this is that magnetic fields are cancelled thus lowering the inductance (and overall impedance) of the wiring and rejecting common mode noise. It shouldn't make a difference if it's done in conduit or plastic.
As far as twisting the branch wiring, I think it's a very good idea, especially for high current draw equipment (I have done this for my dedicated amp circuits). The thinking behind this is that magnetic fields are cancelled thus lowering the inductance (and overall impedance) of the wiring and rejecting common mode noise. It shouldn't make a difference if it's done in conduit or plastic.