1) Plaster ceiling can go how low before it feels too low?
I can tolerate 2.6m ceiling height if you dont have ceiling fan. Also you can maximise aircond efficiency by playing with ceiling height as there's less room volume to cool when you got a low ceiling.


2) Are these kind of designs timeless? Let's say 20 years from now?
I dont see why not. But do know plaster ceiling have quite a short lifetime. The ceiling frame will rust and need replacement. ~10 years.

3) 20 years ago (let's say year 2005/2006), anyone remembers how was the trend that time for lights and ceiling design?
LED lighting was not common back then, fluorescent lighting was used and these have high profile (not flat like LEDs).

4) Or easier to stick with normal ceiling with beams i.e. no need do plaster ceiling? And btw my upstairs hall and rooms/bathrooms are those typical ceiling with lines (can't remember what's the term called).
These are UAC or Plywood ceiling. These last a very long time but it's hard to patch if you need to change lighting and such. Plaster ceiling you can just plaster back the holes, putty and repaint. Plaster ceiling is safer than plywood ceiling in term of fire safety btw.

Government project stopped using asbestos 1999. So your ceiling probably cement fibre board.

If your house humidity not too bad, your plaster ceiling will last more than my stated 10 years. Probably by then you'll want another round of refresh to cater for new wiring/aircond/lighting so I dont think it's a huge issue.

Yes, about 9 years old. Car porch ceiling already disintegrated and 1 ceiling board jatuh hit and dented my car hood. I'll probably replace with UAC in the future.
It's landed.

Yep this. My roof a bit leaky and this can stand some water without issues.

Can consider also. I've seen some around and they do look atas.