I am thinking in other directions.
The optoisolator is very good.
An other point of interest is the power supply for the Arduino. If that is 12V, the voltage regulator might get hot. And heat on the board might reduce the life time.
I hope you have a fly-back diode to protect the mosfet ?
A snubber circuit will further reduce voltages peaks. It can be a capacitor over the motor, but I prefer a capacitor and a resistor.
Starting the motor without a ramp or with a ramp does not make a difference in my opinion. The mechanical wear on the motor itself will not be a lot different. A pwm signal introduces higher frequency vibrations in the coil. But it is impossible to say if that would be bad.
You have to buy a good quality motor.
Suppose you have a very cheap motor, that runs at 12V beyond the border of its specifications. I think most 12V toy motors are like that.
A stepper motor needs a driver. Perhaps the extra electronics of the driver will break down sooner than a normal DC motor.
What about the gear, the rollers and the tube ?
In my opinion the motor is not the problem. The gear might get dirty and the tube will break some day.
If you want go over the top, have a look at brushless motors. They will even continue to work under water. But they need a driver, and again, extra the electronics of the driver might reduce the life time of the project.
I have very cheap 12V pumps, to be used for blood pressure meters. They are designed to be on for only a short time. I suppose the copper commutators are weak. But they run for hours a day for a few years now. I guess I'm in luck.