If you can I set the number of pulses on a pin its really easy. I just dont know the programming. its 3 wires on the pi 2 can be used for all pumps, and the 3rd is unique per pump. so wires needed for a stepper is x+2. where is number of pumps. I'm building a board with all this built in and will be hardwired to max microstepping. which is as simple as bonding the 3.3volt to where pins 14,15,and 18 go on the driver. wont need a reverse so pin 20 isnt needed. so 3.3 volts for all dosing pumps and ground for all. then just the step pin for each individual pump pin moves 1 step per pulse on the pin its connected to. so 4 dosing pumps piwould use say the 3.3v pin and a ground and then 2,3,4,17 for the step input. but the board im designing is also gonna have relays that can run off 14,15,18,23 while using the same 3.3v pin and grounds. I have transistors and running it off 12 volts since thats what is needed for the stepper motors. also might use a voltage regulator and transistor to make the 3.3 volt rail stronger. (more current (ma)) so I dont burn the pi out. Below is a picture showing how to connect a stepper to a pi. but they have it adjustable microsteps by enableing and disabling pins 14,15,18 and it uses pin 20 for either clockwise or counter clockwise when set high, and the reverse direction when set low. Im just gonna tie it to either high or low once I see which way is spins the pump. all steppers spin the same when connected to the stepper driver so once I figure it out for 1 I can make all them the same and then order the circuit boards I've designed. currently set for 4 pumps and 4 relays, thinking about getting a pca9685 and seeing if I can get that to work once I get the basics to work. if I can Ill design it around an 8 and 8 setup with the chip built in so its only a few wires from the pi to the control center. I just dont know how to control the programming of the pi to control the steppers. and if I did i couldnt put it in your program. Hope Im not over bearing.