Thank you. Well done! ... Very informative and clearly presented, both visually and verbally. I don't have your space and facilities, but I'm going to try to propagate Begonias using leaf cuttings.
Sorry but this is not working with your begonia. They maybe get some roots but they will never grow little new plants. You can do leaf cuttings or part leaf cuttings with begonia rex but not with yours (B. cascade rose)