You'd be better off using 1 larger cylinder. running more that one in unison is more difficult that it seems and a load of 250 lbs. is no problem for a decent pneumatic system.
Like motionrat said, stepper systems are good when price is a primary consideration. They are easy to set up and in a burning application they wouldn't run into problems with missed steps which can occur when larger driving forces are required and the stepper motor selected is too small. Another...
