How can you build a reliable turbo supra, 3000gt vr4 or 300zx turbo that wont break down on you eight away?

Lots of money. Each car has their own weak points which need addressed as the power increases. That is a very broad question. You should ask one car at a time, someone who knows the platform can give you details on which parts need upgraded/reinforced & at which power levels in order to make a reliable car. For the most part, these cars are prone to problems & very difficult to make reliable w/ a decent amount of HP.