Stepper Spec , Etc

Hi,

Firstly, thanks to all who replied to my earlier post on PSU for my
first project, especially Terry and Robert Campbell. Excellent info
and I am ordering the parts to get started. I still can't quite
comprehend the "dropping resistor" I need between the driver and
stepper motor. Is there a general size used or do I need to
calculate the exact spec for my intended setup?

Also, I see on the CNCKits website they use a pre-charge circuit for
the power on switch in the power supply. This looks fairly
straightforward. Are there any links on how to wire this type of
circuit and the resistor to use ?

Finally (for now :-), The engineering logic I have applied in
specifying the Nema 34 700 oz inch motors is pretty lame, in that "I
think they look big enough" Is there a more scientific approach to
calculating the torque required (without specialist equipment
hopefully). My first step is to try and couple directly to the end
of the old lathe leadscrew shaft, engage the carriage split nut and
have a Y axis solution. Does this sound a bit too ambitious?

Please let me know if these questions are too basic for this group.

Thanks guys