That's about 200,000 miles.
The stock Nissan head gasket works for 20+ psi, I have also used Felpro but many people say they have had trouble with Felpro.
For fuel, you can upgrade the injectors but you will NEED to modify the computer, otherwise you'll run too rich, or not run at all. You need to swap to an aftermarket ECU, or chip and burn your current ECU. redz31.com has more info.
As far as turbos, it depends on what power you want, not boost level. You can run 14 pounds on the stock turbo, but it won't be pretty. I ran a t3/t04e at 18 pounds, and made 390hp, 440tq... with room to spare on the turbo, but my 440cc injectors were maxed out.
The stock turbo manifolds are pretty decent unless you are making gobs of power.