Spend some time reading the technical bulletins at Alfa Romeo Bulletin Board & Forums
Dunno who compiled this, but it is a godsend when your 164 exhibits one of the many symptoms common to these cars.
You had asked about parts availability - it isn't a huge problem, but unlike your BMW, there is no local dealer - everything has to come via UPS. The two major US Alfa parts suppliers - Centerline and International - have a lot of 164 parts. DiFatta Bros seems to go more in-depth for 164 stuff. Vick and AlfaParts also carry some 164 parts (am I forgetting someone?). There is a "Vendors" section here somewhere on the BB that gives contact info for these folks.