As said,
1) look at all the regular things - you may want to get a mechanic to inspect it for you.
2) Easy 200,000 kms before major failures if left standard but be careful since most imports will have their odometers wound back in Japan.
3) 10psi is the maximum you would be able to run with the standard cooler. Better to run standard boost until you upgrade to a better cooler. A GTT cooler will bolt straight on and let you run 10psi safely for real cheap. A front mount would probably let you run 12psi on the stock turbo. I wouldn't push it further than that.
4) dont bother, its more trouble than its worth, just buy the car you want from the start. same goes for auto/manual and turbo/na. Dont kid yourself into thinking that itll be cheaper to "do a conversion" cuz it isnt.