Great that you got XPresso working. 🙂 I'm always happy to help, but I know the feeling of setting things up and knowing what is happening.
For now, I would leave the Filmtools alone when in Redshift. I have filed a report yesterday, so fingers crossed that this is working soon.
My tip would be to use the Focal length and the Shift parameters so that you can reset those.
When you work with a 21mm, I assume, going by the provided image; you know already to handle distortions with the image. As I write in a forum, I like to mention those things as a general tip. If I knew which practical lens you have used, I could explore what kind of distortion it had, if there is a test anywhere. Sometimes these lenses have barrel and cushion distortion mixed with a "Mustage" distortion, which needs extra care.
There is a lens distortion workflow in Cinema 4D, and you get great results with enough care (i.e., enough lines in image five and more).
All the best