Question: Do you wear the pack on top of your shoulder bridges?
You don't need to wear shoulder bridges as they are covered by the pauldron. You can't see 'em, so why wear them? If you do wear the left one, the straps go under. Actually I put the straps under the shoulder bell->chest strap.
BFG - I cradle it in my arms like the Orange pauldron dude as they walked onwards in Mos Eisley. Else you can put the butt stock down in front of you and rest your hands on the muzzle. Else, carry it over the pauldron, with the butt forward.
For the shoulder pouch - you can either affix it to the pack strap or else use a little velcro on the chest place to help hold it in to place.
Moving the head - if you have trouble moving your head, then perhaps a little more padding on top of your helmet to lift if up more. Or, use some more velcro to secure the pauldron closer to your chest & back plate. Usually it rides up and many sandy's have some velcro to hold it down.