I think that you will need an H-bridge motor driver for each actuator. The H-bridge allows for motor control in forward and reverse. An Arduino cannot supply enough current to drive a motor. To choose a driver you need to know the rated voltage (12V?) and the stall current of the actuator motor. Find the stall current on the data sheet (if you can find one) or estimate the stall current by measuring the motor winding resistance and using Ohm's law to estimate current (stall current = motor supply voltage / measured resistance).
As to running multiple actuators, how many is multiple. Be aware that you will need an external power supply capable of supping enough current for as many actuators as will be running at once.
If you want to start all your actuators at the same instant then your power supply must be capable of supplying the total start-up stall current. If, however, you can tolerate a short delay between actuator starts then the stall current demands will be somewhat less. If you are using an automotive cranking battery as the power supply then start-up stall current shouldn't be a major issue as such batteries are designed to meet short-duration high-current demands.