Would it be less expensive to use exposed steel trusses between the LR floor and the BR floor? Then just use some reclaimed wood planking between? This would allow for better air exchanges between the floors, maybe reduce the amount of ducting needed for two (more insulated) separated floors. Also, we could hang whatever ducts we used between the trusses, without framing the chase with wallboard to hide them. Any other wiring, & plumbing could be exposed, too; wiring through conduit can look architectural, although the plumbing might need extra design, since it's usually PVC, without intrinsic charm and can be noisy when flushed…. but it's worth looking at. This also makes for easier updates and repairs if the infrastructure is exposed.
Wall: Wood, not wallboard.
Q