Pulling to the left could mean the front calipers have corroded and the pads are no longer moving on the sliders correctly, Autolusso will refurb them for about £120.
Keys is not a big deal, and even less so if you have the code card. Apparently the master is required if the imobaliser losses the keys, personally in over 10 years of Alfa and Fiat ownership I've had no need for a master key. This has been discussed before and I researched it, worst case might be an £80 bill to recode the imobaliser and if the ECU has a problem then you probably need a new one anyway.
I don't fully understand what you mean by a gap on the window, misalignement is very common since the windows are framless and there are threads on here describing how to realign the windows if this is what you mean.
How was the clutch - light/heavy? Were the idler bearings and tensioners changed at the same time as the belt?
The pictures make it look good and all in all it sounds like a good car.