Here's what I know, others may have additional information:
- of the two timing chain guides that typically fail, one is able to be replaced by the equivalent guide from the RS4 engine. I don't know if that RS4 guide was ever installed in the S4 engine from the factory. I've heard that the other guide was replaced by one with "better" plastic but don't know that for sure. In any case, checking those two would be cheap insurance if you already had the engine out to swap it over, and would only require the torx drivers
- I had a third guide break: the main crank-to-idler chain guide on the passenger side. It was still working ok but the end of the plastic closest to the crank split off but was still in place. You wouldn't hear an audible difference in this case and it wouldn't affect timing if it just had a split like mine did. Still, I replaced mine since it was "broken"
- Cam adjuster sprocket's pin hole wallows out. I don't think this part was ever upgraded, so again you'd want to check them both if you already had the engine out. For this check, you'd need the timing tools and the M14 or 16 triple square driver bit and a 24mm wrench.

So to answer your second question, you'd need to check those components while you have the engine out. If all the components checked out ok, you'd only be out some hardware (torque to yield bolts), some sealant, and a lend of the timing tools and the triple square bits if you don't have them.