I own a gtr, i'll just add. if your going to do a full exhaust from turbos back, which will require you to pretty much remove the turbos to fit the dumps anyway.. (unless its easier on a stagea tho i wouldnt expect any more room in there) your better off saving up around 2500 for some 34n1 turbos
the standard ones are not a great idea to have sticking around if your going to chase a bit of power.
as for the exhaust/turbo outlets, there are plenty available and most are rather proven, split or unsplit is really the option.
i use the trust split dump/front pipe in one. its a pain in the ass to fit, but seems to be the goods as the split is very long.
other than that tomei, hks, power enterprise and this list goes on and on even the xforce ones are pretty good, but are just hks copies.