Depending on your pulley and belt layout you might just need a new belt, or you might need a new water pump pulley and two new belts.
If your water pump and power steering are run off the same belt, and the ac and alternator are run off the other belt you will need the new water pump pulley and a new alternator and new power steering belt.
Replacing the cat with a straight through pipe is easy, 3 bolts at the front, one bolt on the sleeve connector at the rear. You will need to remove the lambda sensor from the cat and put it in your new straight through pipe. Depending on how long the sensor has been in the cat they can be tough to unbolt. Remember you will need a cat on cars after 1992 to pass the strict emmissions tests associated with cars supplied with a cat. Its not illegal to remove the cat as long as the car passes the emmissions tests.
Paul