Well, the one thing I thing you haven't grasped is that you should not be planning a multiple night trip to fly a paraglider in the Himalayas if you don't know how sleeping bags are rated!
If you are an experienced enough paraglider pilot to take on multiple overnights in the Himalayas, using a very lightweight single skin tent, but you haven't got a clue about sleeping bags, you will probably just die
Surely you have been doing multiple night flights in the Lakes, Snowdonia, the Cairngorms and the Alps? Why not use the one you have been using on your multiple night training flights in the winter?