is it work with arduino mega and how many BWM pins will be available after add it

If I am using only three motors (M1-M3) on my project, would pins 6 and 7 (ie M4) then be available for other input or output purposes? In other words, does the fact that those pins are still connected to one of the TB6612FNG's mean that they really aren't available for other purposes?

I'll add I'm still kind of new to this and I think this type of driver is for a DC motor rather than a DC stepper motor; so if you do try and use an off the shelf peristaltic pump pay attention to what type of motor it has in it.

Just need to provide a battery that can reach the starting current.

No, the power jack only gives the power for the motors, it can't power Arduino board.

What kind of lidar are you using?

Yes, of course. There will be 4 ports, digital pin 2, 9, 10, 13 available as PWM after adding it .