Phew! Tough design criteria Chrissy.

The structure is top heavy and vulnerable to wind loading and uplift especially since it is open below (carport).

Hammerbeams are notoriously poorly implemented, their design is inspired by the great european cathedrals where massive stone buttresses were required on the exterior to resist the subsequent horizontal forces at their bases.

Finally the floor (carport roof) is a long span and will probably require a manufactured wood or steel beam.

Your location will also have a significant bearing on the design. Hurricane, flood, seismic, snow loads, soil?

If you are concerned about the cost you might want to reconsider some of the criteria and I would strongly recommend a specialty timber frame engineer, you can find one on the Timber Framer's Business Council website www.timberframe.org