Yes you are correct that the adjustable loop does not go through the whipping on the end. I would go with your second option simply because its hand to have a detachable ridgeline on the WBBB. When sitting in it, the RL is at your head so its nice to be able to get it out of the way. The 1.75mm line would be ok but it depends on how you set up. Typically the RL sould not be that taut and you should be able to bend it a little however if you come across trees that are too far apart and you cannot elevate your attachment points high enough to achieve around a 30 degree angle, then the RL will have more force applied to it. The closer to parallel the suspension gets the more force is exerted on the suspension and RL. I think amsteel is good for strength as well as it is a little easier to splice than smaller line.
Don't know if you've seen this thread but it would give you a chance to see some different set ups and meet some Ontario hangers.