I fight lost wars, see light, fear sight
I open my mind, need flesh, fear mine
When reversing my car must be firstly at zero, so must I firstly spend a turn setting my speed to zero?
Yes. Also the same situation applies when you change from reverse to forward.
With three-point turn must I also do the same? i.e. Move to zero, then on my next turn move to three-point turn?
Yes. Although you may perform a Three-Point Turn, whenever you are at zero, it's only your speed which is classed as zero and not the marker which must be on the relevant space.