Stepper Voltage and Current question

I am currently starting to design my stepper drive and wanted to make
sure of a couple things. I hate to see smoke. First off I have 3
volt, 2 amp unipolar stepper motors.

1. I plan on using 25 volt supply, is this enough or should I jump up
to 50 volts ? I read I can go 20 times the rated voltage.

2. As far as current limiting goes, since I have 2 amp motors, from
what little I found from reading, does this mean I can run 2 amps
through each of the 4 coils <what I read> or does this mean I can
run .5 amp through each coil ?

Thanks for the help
If anyone is interested in what I come up with when I'm finished I'll
be more than happy to post it.