It seems that on the 1 story 20x30 the attic space has a ceiling height enough for a spare sleeping area. Maybe a Dormer. The bedroom wall below can become a load bearing wall to make up for only a 2x8 joist. I want to keep all the living room open as planned. maybe increase pitch to 12 or 14/12
Yes, this could be done. You might want to use a ladder stair and increase the pitch of the roof as you suggest. You could keep the open beam trusses over the living area.