1. The 65mm version is fixed-focus only, designed for 8/65 Super-Angulon in 00 shutter. The 6.8/65 doesn't come close to being able to cover 4x5, it's really a 2x3 lens, but you could use it if you like massive vignetting.
The 90mm version with focusing mount is as you said, the focus mount accepts Copal 0. Other lenses will fit, some may focus past infinity (or not hit infinity) depending on the flange focal length compared to that of the 6.8/90 Angulon.
2. According to the most recent update the mold designs are finalized and mold construction has started. You should have asked about these kinds of features some months ago. You might be able to hack the camera to do this, it's just plastic. But honestly, why not just use 4x5? You can crop in scanning or printing, or in the worst case cut the negative to 6x12 with scissors!