this is why when purchasing a car have it throughly inspected, get the car racq, inspected by one of there stations, never trust any1.
if u had it cylinder tested it might have shown up that there was low compression in the cylinders.
and u would have seen that the tyres were getting down to the wear lines on inspection or if not close to it before u bought the car.
its not your fault about the wheel nuts but it pays to double check even stuff like that, when u pick up your car from the tyres shop, as i said, never trust any1, they wont care about your car like you will.
in the other respect though, now u have a fresh rebuilt engine (pretty much new) new tyres on the car, now i shouldne see anything going wrong with it if u properly maintain the car from here on out.
do a service every 5000KM and then get a reputable mechanic to check everything on the car, even down to hoses, belts, look for leaks, wearing parts etc then he will let you know what needs to be replaced before it happens, its prevetative measures that keep a car running without a hitch.
im sorry to hear you had a bad experience, but dont let it ruin your experience, they really are a great car, its just some ppl out there dont treat there cars right, and therefore these things happen.
i hope u have better luck in the future if u decide to keep it.