The absolute dimensions of the pattern are not directly significant other than how they appear in the camera view. However, it’s typically expected to fill roughly half a letter sheet.
More information here:
I believe there are different instructions for fisheye and non-fisheye. While the video is good for explaining the process for capture and tips on how to do it, I’d suggest following the actual prompts in the software.
Also, I haven’t seen it stated elsewhere but I’d suggest focusing the camera to the typical distance you expect to use the camera and hold the card at roughly the same distance.