VWRs aftersales can be somewhat sketchy due to their racing commitments from what i gather, plus alot of their stuff seems to me to be rebadged with inflated prices. their racing suspension is KW with their own spring ratings. (Could well be the same though,just recoloured, who knows)
The KW V3s are very good indeed and ride very well. they are awkward to adjust once fitted though. the bilsteins can be adjusted much easier once fitted as the adjustment knobs are at the base. Also there are PSS10's out now.
Reference ARBs, the eibach even with the front on soft and rear on stiff gives a very neutral handling car. I was close to buying a new larger rear bar to make it more rear biased before is old up. if your coming from an M3 id say you want to go for a more rear biased ARB set up. Id be tempted with the whiteline front and rears myself. The WALK is a very good bit of kit, or maybe Whiteline adjustable front ARB, with the BSH rear 27mm adjustable ARB.
If your after a really good chassis, id say you also want to consider the TT lower control arms (some for sale for bargain price in the for sale section). this allows more adjustablity with you front camber as well as les unsprung weight.
You might want to look into a diff, coming from high end RWD super saloons you'll be used to great traction.
What is your budget for the chassis.
Also if your interested in what an Ed30 can manage with just an exhaust/intake, fuel pump and remap then have a watch of these. They really are quick cars, on the std turbo you'll hit between 330-360Hp for only around about £2500
GIAC Stage 3 (Revo Stage 2+ equivlent), so HPFP, TBE, Intake, FMIC and software... V's
Modded E39 M5 (440+bhp)
Modded 135i
E46 M3 (Missed gear, but still got it's ass on a platter anyway )..
Still can't help but be impressed with what a modded KO4 can compete against TBH As you will notice, these aren't a short blast either and speeds get to around 150+ AND IT'S A HEAVY ASS 5 DOOR MANUAL!!!