Lifespan is qouted at about 100,000 full strokes. Mounting position should be shaft end down so seal gets oil. One of mine is up and one is down, and my arrangement puts some side load on the shaft. So I expect the life of one of them to be quite short. So we'll see, but a replace once a year or so wouldn't be too awful.
I used to build pneumatic packaging machinery using cylinders like you used. I did away with lubricators because they made more mess than they did good. However I always shot a bit of air lube oil in both ports on the cylinders before attaching the lines. You can get 3 to 5 million stokes on those cylinders. We easily put 5 million strokes on in a year.