'91 Audi Coupe tune-up

["Christopher G. Gharibo, M.D." <gharic01@mchip00.med.nyu.edu>]

Several questions to the list:

I just replaced the NGK plugs on the Coupe with Bosch F6-DTC, as
recommended by the manual.  Are there better plugs available for this car? 
They were trying to push the AutoLite double platinum's on me, but I
resisted.  Another shop liked the Bosch Silver.  Any one on the list with
more insight on these plugs?

How frequently do you change the fuel filter on the Coupe?

How frequently do you change the timing belt?

Besides the air filter, plugs and fuel filter, are there other items that
you routinely change with a tune up?

Sorry for the string of questions and thank you in advance for your reply.

Chris