Start by having a look through the modification's catalogue;
http://www.mk5golfgti.co.uk/forum/index.php/index.php?page=modsOnce you get a flavour of what brand you fancy, maybe worth dropping one of the manufacturers directly to see if you can mix and match some springs and dampers. I'd of guessed that the 4wd shouldn't cause too much of an issue and perhaps normal GTI dampers with slightly stiffer springs (to deal with the extra 100kg+ you have).
I'm interested to know what you end up doing, as 4wd conversions seem to be getting more popular as parts become available from scrapped cars.