Hi,

For a hydraulic dyno with manual brake control, you do not need 200 pulses per second. Anything above say 10 pulses per second is fine. 

To your question: It is very important that the pitch is constant, otherwise there will be noise on the RPM. I do not recommend making a trigger wheel by hand, you need a CNC machine or just buy one off the shelf. A steel timing belt pulley works well. You may need to remove every other tooth or so.

If you can, I would change the gearing so the pump runs faster, but that's maybe not possible for your kart setup. With higher pump RPM you can go down in pump size (cheaper).