Open floor plans and vaulted ceilings are a part of the very nature of the post and beam construction style. This means you can choose your floor plan based on your preferences, not on engineering requirements.
This is due to the way the weight is supported. Post and beam buildings are built with bents that consist of horizontal beams and vertical posts. The post is the only supporting element touching the floor. In contrast, stick frame buildings transfer the weight from the trusses to supporting walls, which in turn can dictate much of the floor plan.
Additionally, because of the way the bents are structured, adding a loft (or second floor) is extremely affordable. The framework to do so is there regardless, so it’s just a matter of adding loft joists and flooring.