Google is your friend on this one
You really need to do a bit of homework on this as it's very doable but not for the faint hearted.
I did this about three years ago, i found the best way was to pull various little snipets from different write ups from various mk5/6 sites, as there was no definitive start to finish and most of the info i found at the time was from US and Aussie sites. Here's one to get you started
http://forums.vwvortex.com/showthread.php?3552517-Golf-V-GTI-OEM-Xenon-Installation-CompletedA lot of the info i found is bundled up with the whole retrofit of xenons, so info regarding the levellers and headlight washers, as well as the light units themselves.
Regards some of the questions, from memory
1.Holes are pre drilled, the installation is done on the passenger side, so loom and everything runs down that side.
2. I had a custom made loom, so unsure about the Kufatec
3.Mine went behind the the cubby at the side of the dash on the passenger side, there's a little mounting point for it there, as you say i think it is the OEM location. Basically the opposite one from the interior fusebox.
Regards the numbering on the Kufatec loom, if it was me i'd be onto them to sort out better numbering or replace
I had this written down from my installation
CECM block A pin 2 – Power
CAN Hi – Pin 16 – Green & Yellow
CAN Low – Pin 6 – Yellow & White
It might help at some point
Good luck, i have to say it was one of the most rewarding retrofits i did and i've done most of them.