370/g37 test pipes should bolt right up to your v6 FX (they dont on the FX50 - flanges different on header -> cat) $524 seems fit for a brand new set of resonated test pipes like th eons you linked. I have a asset of GTM Resonated Test Pipes from the g37/370z on my FX50 and they are great quality (though I had to cut them up a bit to fit correctly - again I think this is only because I have the 50 - they should bolt right in v6 to v6)
the GTM RTP are $360 from their website.
As for the tune, I would wait until you something more than test pipes and K&N filters. You're going to end up spending $500ish for test pipes + install + $600(?) for a tune to get 10ish horsepower / 10ish tq (and yes, an adjusted power band etc etc) which is not enough to "feel" (though the adjusted power band may feel different/better) so maybe think before spending $1k + for 10 hp. If you're just looking for sound, throw a different muffler on that you can get for much less than $1k and leave it at that.
The 370z guys usually get around about 25hp out of good intakes (like Stillen Gen3 for them), test pipes, and a good cat back exhaust + Tune. 25 horsepower on our fx is going to do less than on a 370z. I am not sure it is "worth it" to spend all that money for 20 hp. I made that mistake on my FX35 back in the day.
However, if you insist, go for it. Ark are a reputable brand. The stock intake is generally satisfactory since it already takes air from the grill. A 'better' filter like you mentioned would help with flow. the test pipes, though resonated, will help with HP but you will lose some low end tq even if they tune it to smooth out the power band, the gains will be high in the RPM range and you may "feel" slower off the line because of the way they tune it. The sound from RTP will add some grumble tone and shouldn't add much drone if they are resonated but I have not heard the ARK RTP in person with a stock exhaust...