You need either a 50W ballast and globe kit (IMO these are too bright for road use)
or error cancellers for the hid kit to work correctly.
the 35W kits are already 3 times as much light as halogen, with a 50W kit it would be overkill (IMO)
And you will need hid globe holders for the mk5 headlights.
I found a kit that has 35 watt ballast that has built in error correction,
Has the mk5 globe holders already and they have 4300k (oem colour temp)
And the 6000k colour temp units. (i used the 4300k, as i had tried a 6000k kit in a previous car,
and found it was too blue for my tastes) if i could, i would have 5000k.
i went with the 4300k colour temp, and i find it's great.
4300k is more light on the road than the 6000k kits too.
kit
this kit uses the same Philips globes.
they don't have any 4300k kits listed at the moment, i would shoot them an email and ask about them.
of course if you want the 6000k kit, than by all means go ahead and get one.
this kit appeared to be top quality when i fitted it. it was only down no my mistake when installing that
led to it being replaced. (i accidentally sliced into one of the high tension wires that run to the globe.
even with that slice, the light still ran for about 6 months.
Jason.