Thanks all for your help and replies.
Just an update... bit the bullet and drove the car 1000km or so to get a proper mechanic that knows what he is doing to look at it. This was after a crazy few weeks of everything seeming to break on us (previous owners must have had some good tricks up their sleeves because we were absolutely taken for a ride with this).
Hasn't overheated again (see my post on head gaskets), water puddles are from heater o-rings, shakey ride is from ball joints (CV joints? can't quite understand the turkish/english translation) and also drive shaft was damaged. The catalysts need replacing, pistons have been cleaned and found not damaged, spark plugs and wires will be replaced as well.
Previous owners did a really good job of sucking us in and lying through their friggin teeth (also the mechanic that checked it for us). I want to take them to court (I am so angry). There were no crash reports on the car but apparently the passenger airbag is missing. There was a dent in the dash, but after repeated questions to the previous owner and the mechanic regarding this, they assured us it hadn't been deployed. Well, it has. All the lights on the dashboard don't light up nor does an alarm sound and our mechanic said it has been rigged (that the previous mechanic said were normal). I am still a bit dubious as to the presence or not of this airbag...
Anyway thanks a lot for your help, I really appreciate it. I will be selling this car (if I can) because I just don't have the cash to throw at it anymore.