for an 18, two 6" flared aero's will probably work the best. For two Type R 12's I say one flared port. I'm just going by what is in your sig... and my personal preference.
well if you have room and box enough, you could probably do three, that would be like 6-7 4" aero's, good luck with the 150's, at the kick its def possible... dash idk.