how can I run six separate stepper motors on arduino mega
Get six suitable drivers and capable powersupplies, connect and run.
SIX stepper drivers, 12 pins (direction & pulse).
Are stepper motors the right choice ?
What’s your project ?
You can use an I2C Stepper Driver:
You can control up to 16 stepper motors using only three I/O ports on the Arduino.
I am making a bionic hand and the stepper motors are for the fingers and one for the wrist
How heavy will the hand be? What will the hand do? Can the construction support torque from stepper motors? How will you identify the beginning/resting point for the steppers?
I wouldn't recommend using this board. The l298 is an ancient bipolar driver with much power loss. And most stepper motors are current driven an cannot be used with this driver. It can only be used with voltage driven steppers.
As already posted, there are many questions that have to be answerd before one can give an answer to your question. And what steprates do you want to achive? I think with a bionic hand you might need to drive them all in parallel. Maybe servos are a better choice?