Hi all,
I'm' new here and am hoping your combined expertise can help me with a wheel/tyre question i have. Firstly, my car is a 2000 A4 Avant 2.8 Quattro and its the muts

is my first audi and i'm loving it.
Current wheels/tyre = 16 std audi alloy, with 205/55/ZR16 Dunlop Sport 8000 rubber.
Am contemplating a new set of alloys, i've seen i nice set of RS4 replica's, 18 inch. But i was wondering would i encounter any problems with these, and also what tyre size would be recommended? i imagine that deviating from the optimum rotational diameter of the original wheels would have soem adverse affects? increased wear on drive train? increased fuel consumption? any thing else?
If thats all a loud of rubbish then thats cool, but what tyre size would you suggest for the RS4 rims?
many thanks in advance for any help guys, sorry for the excesive rambling

just dont wanna stuff up anything with my lovely audi
James.