Groovey, your questions made me rethink some of my own conceptions about tectonics and plate movement and go back to the drawing board on my own "fiction planet". Thanks for that!
From start, I chose the ignore most the times that plates movement is always rotational around a fictional pole (called Euler pole). I thought for larger plates, the rotation would be very small and thus we could think about it linear terms. However, on second thought, that's not the case and it's very much the opposite. Large plates is actually where it makes a bigger difference. So, I looked around a little bit and found this interesting resources:
explaining euler pole
euler pole movement applied to the boundary between north american plate and pacific plate
I also thought of a way to picture this with PS (or Gimp):
- create a layer on top of the the map and place a solid color shape exactly fitting the plate you want to look at
- on another layer draw a little cross to mark the euler pole of that plate
- under <edit>, select the option rotate - a small cross with a circle appears in the middle of the selection
- move that circle to the position where you placed the cross and then rotate the shape
- this allows to experiment with the plate movement and to figure out where subduction, transform and crust formation is happening
(this is an extra effort to get things right and may or may not end up to be useful, I haven't quite experimented enough with it yet - I also suspect it won't work well on plates too close to the poles)