Hi Angelo,
Thanks for your question here!
In the Field Data Editor, you may set the field of view to 10 mm by 8 mm, you can define the field points to cover that desired area. You may set up a Grid of field points for this area:


Regarding the sensor size, you can take this into account by defining a rectangular aperture on the Image surface:

Finally, in order to account for the resolution of the sensor, you will need to use either the Image Simulation or the Partially Coherent Image Analysis tool, where you can resample the simulated image based on the pixel resolution of the sensor. This is discussed in detail in these knowledgebase articles:
Resolution of diffraction-limited imaging systems using the point spread function · MyZemax
How to include detector resolution in MTF calculations · MyZemax
If you have further questions, please let us know and we will be happy to help!
Best,
Csilla