The rule of thumb is 1hp at the flywheel for each 1cc of injector with pump 98 - so the 550/534 size suits -7s or -9s. If you're going to keep the boost down to keep the unbuilt motor safe (ie the 330kw you mentioned) you should be ok. If injector duty gets tight you can just pull the boost down a little further.
It seems to me there's two clear options - Which of these are you aiming for?
1. Cheap - unbuilt motor, -7s/-9s, 550cc, 3 or 3.5 inch exhaust
2. $$$$$ - built motor, -5s, 700cc, 3.5 or 4 inch exhaust, aftermarket gear set to stop third from stripping
Of course if you go with option 1 with -5s you don't have the most responsive turbos, but since its expensive to change, maybe you can just live with it.