congrats on your purchase..
1) Ok, clutches are heavy on the JTD and JTDm, the only time mine was light was after a clutch and flywheel change,its now back to heavy. there are a couple of permanent fixes to this ,thread search is your friend...! in some cases an inconsistency in pedal feel can indicate the clutch slave cylinder is on its way out.a very common fault so worth checking.
2) the windscreen washer leak is almost certainly a leak in a hose ...
3) yeah they do that, again there are some threads where the main culprits have been tracked down and fixed...search ''tailgate rattle''
4) yup, front upper and lower wishbones are practically a service item! the uppers can be polybushed if they are OEM and never need doing again. the lowers are complete replacement as once the rubber bushes wear they cannot be replaced. lifespan seems to be anywhere between 30-75k depending on numerous factors such as driving style and quality of replacement parts, average is around 50k, buy OEM or you will be doing it again in no time.
to be honest only 1 and 3 are specific to the Alfa 147/156/GT's your other issues could have occurred on any marque and can be filed as ''general automotive'' sort wishbones and make sure the cam-belt is up to date and that the water pump was done along with it at the time.
with any luck you should be good to go for a few miles, as a general rule on any used car I always drop the oil and filter and do the air filter and check all other fluids whilst I am in there...In addition a good visual of all of the coolant hoses and turbo hoses is a good idea, as well as a good look at the radiator for leaks /weeps and lastly remove and clean EGR for peace of mind.
good luck with the new car, all used cars ned a little fettling..Alfa's just a tad more so...