Is the intent to "roll your own" or are you more interested in having a PCB mill that you can use to make your own PCBs? For Nema17 I would look at the the Pololu stepper motor drivers and work on a backplane interface for them. Look at how repraps have leveraged these as the plug-n-play drivers for 1000's of machines.

As for the 8mm rods, any place that sells reprap parts will have these, but so does Amazon.com via Smallparts.com. Fastensal also carries metric and are in most metros.