Ok, the white line runs from the jam cleat (where it's probably tied off) thru the block on the rotation limiter, and back thru the jam cleat on the boom.
The double block with becket on the main downhaul system definitely attaches to the foot of the sail, in some fashion.
Finally, yeah, it DOES look you have dual jib halyard tension adjusters, set up so they can be tensioned from out near the hulls as you turn upwind, but you have to be inboard, at the mast, to ease them for downwind. Neat.