can anyone advise me on the following:

1. must each downlight be connected to a driver ?

2. if either downlight or driver rosak, can i replace using any other different brands  of downlight/driver?

3. how does a dimmable downlight works? what are the additional installation required?

4. there is one lighting shop in puchong selling downlights which we can change from yellow light to white light & vice versa using remote control. can also control the brightness/dimmable. 
has anyone used this type of downlights before? any comments?

thks a lot

Any idea how much per bulb and remote from m3asia?

thks for the info..but still unsure of Q2..

btw, is yours led light bulbs? or led downlights?

Different. The downlight designed for bulb has reflectors in it and have narrow light spread.

Pure LED downlight (flat surface) has full 180 degree spread.

If you noticed that bulb in downlight (hole) has dark shadows at the top of wall and ceiling, while LED flat has zero shadows.

You're confused.
Downlight is the housing.
Bulb is bulb (E14, E27 etc)
The link that you posted is LED designed to fit into the old E27 downlight casing. The LED driver heat sink are in there.
Bad thing about it is that if that LED "bulb" spoil, you have to replace whole thing, not just driver.
The newer LED downlight is flat (square or round) with driver outside of the casing.