@TallTanBarbie
You appear to be using the SkyMaxx Pro v4 style of clouds in v5, which has its limitations. One of those limitations is the fact they are texture based clouds. The opacity in them will not change. For most of what you seek, you'd need to use volumetric option, but given your rather large use of 4K displays I don't think it's an option.
Shadows are a lost cause to talk about here as already indicated. Nothing can be done.