Be careful with this - just because you can make the projector do it with the calculator does not mean you will get acceptable brightness onscreen. When I run the calculator with your settings (18' throw, 118" screen size, zoom = 1.33x, screen gain =1.0) I get the following warning:
Recommend higher brightness, reduce image size or increase screen gain.
This is the calculator trying to tell you that despite the ability to physically produce this image size, it may not be bright enough.
118" is going to be pushing this projector's brightness limits any way you slice it. Could you live with this picture? Probably. But I've seen the 700u and the 900u pushed beyond their screen size limits on unity gain screens and its just not as nice.
I don't know that bulb life and zoom are related... but as a rule of thumb you don't want to push the edges of the zoom or the lens shift unless you have to. Both can create subtle distortion of the picture and/or color near the edges of the screen.
If you are dead set on a 118" screen then look at some units with a gain of 1.3. These screens in effect "focus" the light back toward the centerline producing a brighter image, but only within a certain cone from the centerline. Move off of that centerline and the image will dim... much like the older LCD displays do.
Best regards,
~Josh