The third generation VW Cabrio years run from 1993 up to 1997-ish, at which point they started switching over to the MK4 assembly line process... '98 & '99 models are known as the mk3.5 for this reason, as they are still mostly mk3, but have slight differences... most notably the headlights got updated to the rounder mk4 style. The Mk4 was from '98ish-2002.
I imagine any wheel sizes should be similar to the VW Golf platform, which the VW Cabrio is based off of, but I can't be positive of that.