Welcome. You are starting to find all of the common GTV problems and questions. Thermostat is a common problem ( fortunatly seems always to seize open, so no overheating just overcooling). The other exhaust which is not mentioned above is the Cybox system. Do a search on cybox, mij, alfaholics and ragazon and you should find heaps of info. I have a cybox install and review on there somewhere. Search for autobits for stainless frontpipes if they have gone.
The search function will soon become your best friend as what I have found since alfa ownership is that there is few unique faults, we all have the same ones, Which is good as we now know what the problem is and what the easy fix is. Whilst your at it you might as well search for rear suspension bump stops, clutch slave cylinder, and injector warning light ( and the white wiring plugs). You will know in advance when they happen and how cheap they are to fix. They are reliable cars just hobbies aswell. I have only been a v6 owner for 3 months and I havegone through most of the common faults ( which are not that a big deal) and what I have a great car, thats fast, sounds great, everybody admires and...............drinks a lot of fuel ( mainly because its hard not to get addicted to the noise when you ragg it)