Welcome!
I believe there are several on this forum that have modified their mkiv's, both Jetta and Golf. In my case, I've done the grill block and some under-body coverings:
Grill block:
Front under-body (this is the bottom of the front bumper, which I removed to put the coroplast on):
This combines with an engine skid-plate (mine is an OEM steel version, but there are also aluminum ones as well as the OEM plastic under-engine cover)
Rear under-body coverings (closes up the rear bumper "parachute"):
Helga is also lowered by about 1" so that the tires are less exposed.
Would be interesting to see your grill covers.