After Mark's introduction and advice, I contacted the seller to confirm a few things...
...the story unfolds as follows...
1 - He (Paul) says the turbo wasn't fitted properly, and a coolant pipe was blocked, therefore not enought coolant which stopped the turbo from spooling properly, thus causing the smoking.
2 - The leak by the injector was due to the fuel rail not being fitted properly, so now it has been resolved.
3 - Apparently wiring loom was a bit of a mess, so that has all been replaced and fitted correctly.
4 - Coolant pipes (all) have been replaced with silicone hoses.
5 - A Walbro fuel pump has been fitted.
All in all, it sounds like he's sorted everything out I started to get worried about.
The other issues are extremely minor I think. The only thing he's not sorted is the heater (only works on speed 4).
All answers weren't prompted, so I think he's genuine. Like I said, he works for Fiat, so should be a sound car.