OK, S13's, Ive had a fair few, inc one over 350bhp, so heres the low down:
Chocolate cranks - the CA18 IS very prone to big end problems and is expensive to fix
Rust: Under the spoiler, rear of the sills, chassis legs behind the rear wheels, top of the front suspension turrets.
Rear subframe bushes are also prone to failure, again £200 for Nismo bushes (Nissan dont sell them without a subframe) and similar money to fit them.
Turbo gaskets are an easy job (Or at least when you have done it a few times
280bhp is quite possible, but you need a fair bit of stuff to make it reliable, including a metal headgasket, uprated clutch, bigger turbo, Stage2 ecu and maybe bigger injectors and MAF.
Hope that helps