1) My technical know-how is limited to checking the tyres, oil, coolant amd screenwash levels.
Do you need to be mechanically minded to drive an Alfa Romeo 156 without incurring huge garage bills?
Well, the same level of knowledge saw me through 4 years of happy 156 ownership. Two things worth knowing about
1) Twin sparks go through oil - how much varies from engine to engine, but you do need to be in the habit of checking it regularly, more so than other cars I've owned. Mine used to need maybe 1/2 a litre every 1000 miles.
2) The twin spark cambelt interval is 36000 miles/3 years (Alfa UK initially tried to get away with saying it was 72000 miles, resulting in loads of snapped cambelts, which did Alfa's reputation for reliability no good). Bear this in mind when you're shopping around, as many will be overdue, and it's not a cheap job.
As for garage bills, so long as you look after it and make sure it gets serviced, you should only need work on the usual wear-and-tear stuff. Avoid the main dealers and take it to a local specialist - there are some really good ones, and you'll be able to find a recommendations thread somewhere on here.
You get a lot of car for your money with the 156 - what swung the buying decision for me was seeing older, slower, lower specced and higher-milage Golfs and Focuses selling for the same price if not more! Made me realise the 156 was a bargain and solved the head vs heart dilemma