Will this fit my Prusa i3 style printer?

It fits printers that use a standard 42mm NEMA 17 mount and a T8 lead screw on the Z axis, such as many RepRap Prusa i3 clones. Check your screw length and lead before buying, because the 100mm screw is fixed to the motor.

What does 2mm pitch and 8mm lead mean for my Z axis?

The screw has four starts, so one full turn moves the nut 8mm. That is faster than a single-start T8 screw, which moves 2mm per turn, so you may need to change your Z steps in firmware.

Is the integrated screw better than a coupler setup?

It removes the coupler as a source of wobble, misalignment and slipping set screws. The trade-off is that you cannot swap the screw or shim it separately, and a bent screw means replacing the whole motor.

What comes in the box?

The motor with its 100mm T8 lead screw, a brass nut, and a 1m (39.37 inch) motor wire. No endstop, mount or extra hardware is included.

Do I need two of these for a dual Z-axis printer?

Yes. Each unit drives one screw, so a printer with two Z screws needs two motors. The listing is for a single motor.

What torque does it have and is it enough for a Z axis?

It is rated at 400mN.m, about 57 oz.in. That is enough to lift a typical gantry on a bed-slinger style printer, but heavy or binding axes may need more.