height of the plaster ceiling? answer is very clear, ask high as possible. and just like other member say to cover all the beam, wiring, aircond and many other.

As you say, your plaster ceiling after beam is only 8.5ft? not really a problem actually, you still can maximum the height, how? for example, making some design like light box to higher up the living hall ceiling at the center part, but remain the side high to the beam height, then you will have the higher ceiling at the main activity place, do it the same to your dining hall, then everything will be find already