About the running backstay, that is exactly my setup. When not in use the stay is routed via a snapshackle with a short piece of string attached to the scepter next to the cap-shroud stay. From the shackle it goes to a block attached to the same point as the Genua-sheet turning block. At the end of the backstay there is a knot so the line cannot escape the block. The snapshacke position is used to take up the slack in the backstay so the line does not get in the way
When in use the secondary winch on the windward side is free so you can use it to tension the windward running backstay after you release the snapshacke that sits halfway the backstay.
Imagine the whole setup as a triangle with one square corner. One corner is at the spreader, one at the snapshackle and one at the turning block. When not in use the backstay follows the two legs that share the square corner, when it is in use it follows the leg from the spreader to the block. As this distance is much shorter the tail of the backstay line is long enough to attach to the secondary winch.