The auction is for a single wheel so you'd need to look for another 3...
Don't listen to the numpty above, you won't need adapters. Early A3's were 5x100 the same as the Mk3 GTI so they would be a straight fit.
You'd need decent sized tyres to make them work properly, for example 195/45/15's. 185/60/15's are balloons and would make the car look like a tractor.