Depends on your yearly mileage / daily commute distance if you use it as your only car.
If you buy one with the super strut already done then you dont need to worry about it for a good while yet. Turbos are OK, dont go very often but getting your own reconditioned will set you back a few hundred quid, Rear diffs only tend to go when you start drag racing or launching the car alot, gearbox..... if it needs replacing then you can pick up a good second hand one for about £300. But non of the above mentioned is any worse than any other car...in fact my Skoda Fabia Diesel has cost me more to replace parts than the Faff, the turbo went and it cost me nearly £1000 to get replaced....I can only imagine the turbo I could have purchased for the Faff for that amount.
Buy a good one and dont start tinkering and they arnt too bad, its when you start moding when things get expensive. Buy a cheap knackered one then chances are you'll be spending ££££ to put it right.
Mine cost me £80 to fill it up the other day so fuel is the biggest expense by far, the average GT4 (ST205) will do from 240 - 320 miles to a tank full, some get more, some less so you should be able to calculate your fuel costs.
Insurance like every car depends on your age, location and no claims. personally I dont think its too bad but then again it only costs my £450 a year so cant complain too much.