hi, how do you know its valve tappet sound? My car seems gt the similar situation, when I am driving beyond 80kmh, the soft tak tak sound can be heard....

No colored smoke noticed, no oil stains on plug.. What's the problem that cause oil loss?

About 40% according to the observation on dipstick...

This white smoke of yours on cold morning start, is equivalent to 'blue' smoke I enquire about.
As stated above and I quote:

This white smoke indicates your car engine valve seals are hardened , and leaking oil from cylinder head into combustion chamber.
IF there is coloured smoke during acceleration/deceleration, it indicates piston rings are leaking engine oil from combustion chamber to engine crankcase.

You may have a point in water condensation playing a part with white smoke on morning start , though not expressly saying so.For all we know, there may actually be some condensation.
On top of that Senscents seems happy with spark plug conditions.

However as his engine is consuming like 0.7-0.8L engine oil in about 8000 km, plus the fact that 'bluish' colour  smoke is very difficult to 'see' by untrained eyes , hence my position above on valve seal leaks.

Coloured smoke during quick acceleration or quick deceleration , in my humble opinion, would indicate engine oil leaking through stuck piston rings . I wish he can get someone to test this possibility for him.

Yeah the spark plug still holding up after a year or more cant really recall when was the last replacement, as i just service the car 3days ago. Ask the old mechanic, i think he's about 65 years old on the codition of the plugs. He says that it's still good to go, need not change since the engine are running smoothly.

As the oil consumtion still manageable, maybe can save on the repair works. Guys.. How much oil consume to warrant it as excessive & need to repair.
Maybe i'm using the 5-30 oil. too thin viscosity ?