1.how much could i pick up a ca18de/det for? CA18DE $800, det$2000
2.would this be the right choice of engine ? What do you the car to be ?
3.can it fit the ca20e box? Yes but get a front cut and use the CA18DET gearbox
4.i know it bolts up FAIRLY easily but unsure as to what changes need to be made to the wiring loom etc? Ask kingpin, he has done the conversion.
I wouldn't bother putting a CA18DE in, A CA18DET is worth it, but the CA18DE has less torque then the CA20E that is already in the car. Yes the CA18DE has more power, but you also want more torque.