One thing I should mention for the benefit of future users. When the new Duet WiFi 1.02 boards arrive, they will have flyback diodes to V_FAN included. Then you will need to ensure that V_FAN is the highest voltage that any fan will be connected to. So your scheme of setting the V_FAN jumper to VIN connecting a fan between +5V and a PWM FAN- output would still work. But the reverse scheme of setting V_FAN to 5V and connecting a fan between +12V or +24V and a PWM FAN- output would not.
Am I okay to piggy back only the step and direction pins from the test headers to use to signal my external drivers? I am curious to see how the external drivers at about 3 amps may affect my results.
Yes, that's OK, the STEP and DIR pins are driven the same whether the drivers are internal or external. You may need to use the M569 command to increase the step pulse width for your external drivers.
Thank you for the help David! I'm running a test with the external drivers now.
I have the Duet underneath my Kossel with the wifi antenna protruding slightly. If the wifi signal is reasonably strong in the room where the printer will be, then it should be OK to put the Duet underneath the bed, assuming it is not surrounded by a solid metal frame. There is no easy way of extending the antenna, and FCC/CE regulations make it impractical for us to offer a version with an external antenna.