4) The drawing is just a schematic. In reality, could one or two of the internal blocks be a double or MUST they be 2 singles to achieve the cascade effect? First, the 2 on the crossbar could certainly be a double, right? Although only one single is shown for the blue, there must be another that is not shown. Could that be a double? That one might be too close to work as a double, space wise.
The top blocks can be replaced by a double but the two floating ones must be independent. Think about it: as you pull on the downhaul the blue/red block goes down and the green/red one goes up. If you attach them together, nothing will work.
Why do you think there is another block for the blue line? It's just entering by one side of the mast, going up to the block and down to the other side...
