I had all the same work done on my 2001 A6 4.2 last month when I had to have the water pump replaced. The ride has 103K miles so when I saw that all the labor of getting to the WP/ TB/Thermstat etc. was basically covered in just getting to the WP, I had everything I could think of replaced. Cheap insurance at my mileage. Except for the hydraulic tensioner I would replace everything else especially with the AZ heat treatment factor to the parts you have listed.

Side note: my waterpump ended up not being the culprit of the coolant leak, but a short hard "rubber" hose connected to an oil heater or cooler (I don't know enough about it yet) on the passenger side, front end of the engine was dripping through a trail to the front of the block.