Mill Conversion questions

I'm in the process of convertimg my Sherline Mill to CNC. I'm thinking
(at the moment) about running Sanyo Denki 232-180-DB motors with Gecko
210 drives.

If I mount the handwheels on the rear motor shafts so I can run the
mill by hand when I want to, I end up generating voltage when I move
the handwheels, assuming that the motors act like generators in this
case.

Are the 210 drivers sensitive to this voltage, particularly when the
system is otherwise unpowered? Do I need to disconnect the drive motor
cables, either directly or with a relay, when I use the mill manually?
If so, do all of the motor leads need to be disconnected? (That's not
a problem if you just unplug it, but would be a design detail if you
were going to use a switch or relay)

Is there a recommended heatsink for the 210? (I've seen one at the
Camtronics site that mounts 4 drivers) I was thinking about using a
variation on a heatsink system I once saw on a high power stereo
amplifier. The drivers would be mounted vertically on individual
heatsinks to form a chimney with fans top and bottom. My idea is to
get really good airflow for efficient cooling, putting the air where
it it really needed. (In fact, if I used the Camtronics heat sink I
would be really tempted to box the back side for the same reason.

I asked a question like this on the SherlineCNC group and got some
good answers, but not everything I was looking for so I figured I
should ask here.
Thanks,
Chris