if you want to cruise round with your arm hanging out the window and wear a baseball cap with a straight peak, then you might want to go 9.5 wide with 30 ET and some nice Chinese stretch. 
as above, but i'd like to add that with the 1.9TDI having a 50mm strut diameter (rather than the more powerful ones which have 55mm) your coilovers will be pretty worthless come resale time
i'd advise going for some lowering springs instead, but as above it depends on your plans.
in terms of wheels, here's a quick glossary:
PCD = bolt diameter. for PQ35 chassis cars such as your Mk5 this is 5x112
ET = offset. this is the number of mm from the middle of the wheel where the face mounts to the hub
other critical information you'll need is the hub diameter, which is 57.1mm. if you've got a wheel with a bigger hub diameter than this it's advised to run spigots to reduce the chance of wheel wobble. you also need to know the width of the wheels as this affects the stance of the car.
here's some shots of my car on BBS VZs (part of the CH family - now discontinued). i know it's an A3 but you get the idea. the spec is 18x8 ET44 with 225/40 as Audi intended. my car is also lowered on the Weitec Hicon GT coilovers. no rubbing issues unless i'm running 3 up or more:
Pescaras are 18x7.5 ET51. this means that to get them looking like my wheel, you'd need to run a 13mm spacer
hope that helps
