As a starting point i'd probably leave the intake side alone and look at removing the cats first. Cat removal pipes can be bought for approx ?300 and once fitted your car will be a totally different animal.
On a Jap spec car when you remove the CATs you need to keep an eye on the boost level and make sure you don't over do it so a boost gauge would be a good idea. You can restrict the boost level initially by fitting a restrictor ring in one of the CAT removal pipes. Also a freer flowing exhaust system will help release a few more ponies and make the car sound like it should.